Ideally, a roster of about 50 or so guys would probably be perfect when you think about it. When you factor in managers, valets and all that, then it's probably closer to about 60 or so all told.
The only "thinness" I see in WWE's roster is that there are generally 10 or 15 people that Vince has something done with while the rest of them are primarily left to flap in the breeze. As of right this minute, Triple H, Stephanie, Cena, Bryan, Reigns, Ambrose, Kane, Big Show, Rollins, Wyatt, The Usos, Miz & Mizdow and Rusev are really the only roster members that have any degree of priority or relevance. I would include Wade Barrett, but the poor bastard is exactly where he was at this point a year ago: he's Intercontinental Champion, yet he's losing every single non-title match he has. This is a prime example of what a fucking schizophrenic boondoggle Vince McMahon's booking is these days and is exactly why I wasn't interested in Barrett getting the strap for the 5th time. Sometimes, you'll get something sensible and entertaining and sometimes you'll get something that seems to make sense only in Vince's mind.