I do think the roster is overworked big time, and there's a number of causes to it.
Comparing it to the roster of the 80's and 90's, wrestlers back then didn't have to take off near as much time for injuries, like wrestlers are nowadays. There was never a situation where Hulk Hogan, Randy Savage, Jake Roberts, Ted Dibiase, Bret Hart, and the Road Warriors were all out at the same time due to injuries. At first look, it would appear that the wrestlers were much tougher back then than the wrestlers are nowadays. Especially with wrestlers working more dates throughout the year than the wrestlers today. But even with that being said, wrestlers nowadays have it much harder than than the wrestlers back then. There's a number of reasons for that.
1. Workrate in much more intense and physical. Wrestlers in the 80's and even 90's didn't have to constantly work at a 5 star level like wrestlers these days do. Wrestlers, back then, for the most part only had to work really high quality, intense matches a few times a year at ppv's and maybe for the occasional Saturday Night's Main event shows. Plus, not to mention wrestling action in general was much more light and easy than today. There were very few wrestlers back in the 80's that did moves off the top rope. There were much more rest holds. There was much more of working the crowd. I've seen plenty of matches, where wrestlers literally went 10 minutes doing nothing but playing to the crowd and not touching each other once. There wasn't as many intense gimmick matches. In the WWF back then you pretty much only had steel cage matches (which were rare) and battle royals and that's it.
2. More dates on TV. Wrestlers back then worked way more house shows, but it's pretty much an unwritten rule that wrestlers don't have to work near as hard at house shows as they do on tv shows and ppv's. Back then you had 4 or 5 ppvs a year, and about 4-5 Saturday Night's Main Events, and monthly tapings for Superstars and Wrestling Challenge, plus house show matches that aired on Prime Time Wrestling. WWE honestly had just as many tv shows back then as they do now, but the key difference is that wrestlers usually taped a whole month's worth of shows in 1-2 days, and then it was just house shows for the rest of the month, or a ppv on a couple of the months in the year. Nowadays, every week wrestlers have to go to Raw, then do Smackdown and Superstars tapings on a weekly basis, not to mention way more personal appearances, charity events, world tours, etc.
3. More ppv events. The WWE had 2 ppv events from 1985-1987, three in 1988, and four in 1989, then 5 in 1993-1994. Since then WWE went to monthly ppvs, and in this day and age the WWE has 12 monthly ppvs, plus 3-4 Network exclusive specials each year. There's more big shows where wrestlers really have to "bring it" than ever.
4. Wrestlers can't use drugs anymore. Let's be blunt, many wrestlers in the 80's and 90's used drugs and alcohol to either mask their pain, and in some cases heal injuries. Wrestlers didn't just use steroids to bulk up and look like super human bodybuilders. They also used them because they helped heal injuries quicker than normal. Doctors prescribe steroids to all kinds of people (not just athletes) after major surgeries to help with the pain and to heal quicker. In this day and age wrestlers are forbidden from using pretty much any drugs, steroids being the biggest one. Wrestlers can't really heal quickly anymore because they can't use steroids. Thus when they get a major injury that requires surgery, they can't come back near as quickly or even worse, continue working like they could in the past. Wrestlers also can't take painkillers, smoke pot (though technically they weren't allowed to do that back then either, but WWE was much more lenient on it then), or anything like that to help mask the pain their bodies endure. Wrestlers have to be drug free, yet they engage in nightly car crashes on a weekly basis all year long, something the body is just not built for. And with wrestlers expected to work harder and do more crazy stunts in matches these days, it makes it even worse.
5. WWE is far more health conscious in this day and age than in the past. It's no secret that short of a broken neck or back, or a life threatening injury, wrestlers in the past were expected to work through any injuries in the past. Concussions meant little, torn ligaments and muscles didn't matter, separated shoulders, broken bones, etc. Doesn't matter, get in the ring and work. If you could walk to the ring or weren't in a coma, or dead, you worked that night, plain and simple. That mentality thankfully no longer exists, but it also means that wrestlers aren't going to be gone much longer and more frequently. WWE does not play around with concussions, and if a wrestler gets a concussion (which is very likely to happen), they're instantly out for a month. Back in the old days, wrestlers lived with constant concussions and nothing was said. Many of the wrestlers would still rather work through injuries (like Cesaro), but WWE no longer allows them if it's somewhat serious. Obviously if a wrestler has a simple cold, or something like that, they're expected to work. But if they have a broken leg, separated shoulder, concussion, neck issues, etc. WWE will force the wrestler to take time off.
All of those factors are why wrestlers are getting injured so frequently and having to take so much time off.
Of all those factors, I think the fact that wrestlers can't take steroids, painkillers, nor smoke pot or do any other drugs is the biggest reason why wrestlers are injured so much and have to take time off. Like it or not, any of those drugs allowed the bodies to heal quicker (though a huge price would be paid later on as we all have seen over the last 10-15 years) and allowed wrestlers to work through injuries. Now the bodies are falling apart, and the only way to recover is to really take time off. In the long run for a wrestler's health, it's a good thing. As I really believe that in 15-20 years from now, we're not gonna see the wrestlers of this current generation passing away at a frequent rate like we've seen with wrestlers from the 80's and 90's. But it does make it to where wrestlers have to take more time off.
As to what the solution to this problem is, there's a number of things WWE could do.
1. Cut down on the ppv events and big shows. With the Network being the central place for people to see the ppv events, and WWE not relying so much on revenue from ppv buys anymore, there's really no point in having so many ppv events. Cut it down to maybe 5 major events (Wrestlemania, Summerslam, Survivor Series, and Royal Rumble, and one other event; either Night of Champions, Money in the Bank, or bringing back King of the Ring) and have maybe 5 other Network exclusive special events (Extreme Rules, Elimination Chamber, NXT specials, etc).
2. Cut down on the gimmick matches. There's too many risky gimmick matches all year around. It also makes the matches mean less. We shouldn't have 5-6 Hell in a Cell matches every year, or 5-6 TLC matches, etc. Cut them down to 1-2 a year, not only to put less risk on the wrestlers, but also to make the matches feel more special.
3. Go back to doing monthly tapings for Smackdown and Superstars. There's no reason to do weekly tapings for Smackdown, and especially Superstars which is only on the Network anyway. Some might argue you can't do that because of the internet and spoilers. Well, how many people watch Smackdown anyway. Everyone reads the spoilers on Tuesday night before it airs later in the week, and based on the spoilers and what happens, they'll decide to watch or not. So people can decide a month in advance if they want to watch this week's episode. If a show is taped in advance, it doesn't matter if it's taped on a weekly basis, or three month's worth of tapings, the "must see" element of the show will be lost regardless. So go back to taping a month's worth of Smackdown and Superstars episode, so that can cut some of the traveling down on superstars which will be great for them and their bodies and mental state.
4. Yes, WWE needs an off-season. I think an off-season in general would be great for WWE as a whole, as everyone needs time to rest, and the product is stale and over-saturated. There's too much wrestling on TV and too much going on so everyone (wrestlers and the writing team) are more or less "going through the motions" because they're burnt out. And with the Network, WWE doesn't need to be on cable tv on a weekly basis. To keep business going and to keep generating revenue, WWE could use the Network to run new documentaries, new interviews, new podcasts, non-in ring shows for wrestlers to do during that time, stuff to keep the wrestlers on the fans' minds, and also hype up the return for WWE as a whole. Not having weekly tv and monthly ppvs, and no storylines going on will make the fans miss the product and also flock to the Network where the only new product in the off-season will be airing. We may not get to see Cesaro, Roman Regins, Dean Ambrose, or John Cena wrestle in those three months, but they can do shows on the Network both in kayfabe and non-kayfabe form. We can have new Stone Cold podcasts with the wrestlers on them to hype up their returns. Shows about what they're doing in their off-season. Maybe some "road to recovery" shows for injured wrestlers. The possibilities are endless. I would say do a three month off-season in August, September, and October, which are usually the deadest months for WWE. Move Summerslam up to either July, or hold the event at the very beginning of August and make it the end of the year event that wraps up the yearly storylines (not Wrestlemania), and go to a three month break afterwards. Resume the year with the Survivor Series event around Thanksgiving, and then build to the Royal Rumble and the Road to Wrestlemania. In comparison to the NBA, Wrestlemania can be the All-Star Game (half-way point of the season), and Summerslam can be the NBA Finals. I know that sounds crazy, but making Summerslam this important would go a long way in giving WWE a second Wrestlemania-level event, which it doesn't have currently. Wrestlemania is a huge brand all on it's own, so trying to build Summerslam up to it's level of hype and stature won't hurt it in the slightest. If WWE, over time, can get Summerslam to the level of Wrestlemania by getting cities to bid for it, having it happen in stadiums, and making the week up to Summerslam a true event like Wrestlemania, than those profits alone could make up for WWE's three month offseason in August-October.
I would also keep NXT at the exact same schedule, as far as the television product goes. The wrestlers training and learning down there would remain a year long thing. They just wouldn't be on TV either from August-October.
The whole idea of this would be; one: to get wrestlers some truly good time to recover from nagging injuries or serious ones; and two: to make the fans long for and crave to see some wrestling action. If NXT is producing weekly television while the main roster is on an offseason, it won't make the fans want to see the main roster shows and events and talent. Having no televised matches, storylines product for three months, from both the main roster and the NXT roster, will make fans crave some action by the time November would roll around.
5. If not an off-season, then some kind of off-season rotation for all talent. While I think an off-season would be very good for WWE, realistically it's not gonna happen anytime soon. But there's no reason why WWE has to have their entire huge roster not ever get any significant time off. Half of their roster goes to every show and isn't even used anyway. Every wrestler should get a mandated three months off every year. Time away from being in the ring, time away from personal apperances, just three months where wrestlers can spend time with their families, to relax, heal injuries, to maybe do other projects they want to do (make movies, make music, host tv shows, whatever), etc. It should be on a rotation. If WWE has 120 wrestlers between the main roster as well as the NXT roster, then they should have 90 active wrestlers, and 30 being on a three month vacation. Then when the next three months come up, those 30 wrestlers come back, and another 30 wrestlers start their three month break, and so on and so forth. Give wrestlers some time to heal injuries, and to make the fans miss those wrestlers and allow them to come back refreshed and ready to go.
That's my take on the subject.