In Cena's era there was no nationally promoted power house promotion unless he went to Japan. ROH and TNA reach a tiny fraction of what WCW did in it's dying days (TNA's best ratings are half what WCW's worst numbers were, same with PPVs). WCW was the last touring company that regularly did shows through out the US and over seas in comparison to WWE.
The big thing is how long was someone at or near the top of the industry as a whole. Fact is thanks to TBS and WCW Saturday Night Ric Flair was a major star all over the US in the 1980s even without the WWE expansion backing him. Same with Dusty Rhodes, The Road Warriors, and a few others. Back in the mid to late 80s it's hard to think of anyone who could have traveled all over the US and sold better than Flair outside of Hogan. The fact that Flair had at least one reign every year from 1981-1996 is a remarkable achievement. Hogan's run was similar but a bit less impressive in terms of title runs due to the large amounts of time he took off. Cena comparably has been WWE's biggest star, and by extension the biggest star in the Industry in the US, for roughly ten years. He would likely need another 2-3 years before he could break the record meaning by then he would have maintained the top spot for nearly 15 years, comparable to the popularity and staying power Hogan & Flair had at their heights.
I will say given how well Hogan & Flair performed as ratings draws in the final WWE run when both were well past their prime and working abbreviated schedules (especially Hogan) that Cena has a way to go to catch up there. Lets see if Cena can still sell main events when he is 10-15 years past his World Title days. If he does then love him or hate him you have to give him his due.
As for the quality of the title runs, because the industry changed so have the length of title reigns. In the 80s when guys like Backlund, Hogan, and Flair would dominate the title for years at a stretch the live touring was the bread and butter of the show, and it took a long time for everyone in the fan base to have a chance to see the champ as the shows toured. If a champ proved a major draw they held the title longer through multiple tours of the country. Such was the case with Flair & Hogan. By the time WCW started airing monthly PPVs and started airing main event quality matches on live Nitro broadcasts (forcing WWE to change to keep pace) storylines progressed faster and thus titles weren't held as long. Cena has three very long reigns in which it was clear the company was built around him for the long haul which other than HHH is the best any champ has had since the end of the territories and pre taped jobber heavy TV shows. Bottom line Cena has dominated the decade in WWE and been its most consistent ticket seller and merchandise mover. Same with Flair & Hogan in their time. However, with the change in the business model we will never see a run like Flair had where he held the championship for over 70% of the decade in the 1980s and toured the US, South America, Singapore, and Japan (add in Germany if you count his over seas title defenses as WWE champ in 1992). You'll never see someone hold the belt 5 straight years either like Backlund & Hogan did, the business model has changed too much.
And yes, some people nitpick that some of the reigns were extremely short. I certainly hate to think of Cena getting the record when he has reigns that literally lasted less than one full day, but lets not forget Sting also had a reign like that (winning and loising the title in the same episode of Monday Nitro), Hogan had the "Finger Poke Of Doom" and then managed only two title defenses before losing the belt two months later, and Flair had the Vince Russo inspired "Kevin Nash awards him the belt" moment when Russo stripped Flair of the title when he needed time off for injury (re occurance of the ear issues from injuries sustained against Ultimate Warrior). Personally I never thought given how the storyline progressed that Flair's 15' th reign should ever have been considered interrupted but if it wasn't that would eradicate reigns for Jeff Jarret (awarded the title by Russo when Flair was injured) and Kevin Nash (who beat Jarret later that night) and Pro Wrestling Illustrated and WWE seem to not want to do that.
Now of course we can argue that Flair was a bigger star (legit argument, especially when you still even today see him referenced in sports and pop culture, LeBron James giving interviews about him as the "originator of swag", Darrius Rucker giving interviews about him and inviting him to charity gold tournaments, references on NFL Today on CBS, numerous references by the First Take Commentators on ESPN, being invited to address the 49'ers before a playoff game, being invited to speak in the clubhouse to The Boston Red Sox, multiple references in rap songs, one even named after him, etc etc) just as we can argue wether Cena was a big a nationally recognized media star as Hogan, as good an in ring performer as HHH, or if he ever reached the zenith in popularity that Austin hit in his prime before his 1999 back injury. Some will complain that Cena would have had a harder time rising and staying on top if Austin didn't retire early with injuries, if Rock didn't chose Hollywood, just as Austin benefitted from HBK's back injury that forced him out of sight just as he was reaching his peak, as Hogan benefitted from Andre's willingness to put him over clean at W-Mainia or the poor performance as champ of The Ultimate Warrior, just as Flair benefitted from the car accident that ended Magnum TAs career when he was in line for a title run, or the horrible booking that lead to the disaster that was Sting's first title run, or grabbing an extra WWE Title when Randy Savage decided he didn't want to wrestle and wanted off the road while he was still champ (or Brett Hart benefitted for Warrior injuring Flair when WWE was in the midst of a major feud between them seemingly headed for Survivor Series and likely ending with Warrior getting the belt, instead Flair was off for two months recuperating and Warrior got fired, opening the door door for Hart). These things happen to every long term star and it doesn't change how successful any of them ultimately were, plus there is no way to know if in any of those random cases if the star in question would not have been successful in the end, in every case they very well may have ended up with the same or similar level of success, just by taking a slightly altered path.
One thing is certain, if WWE decides to let Cena get the record you can bet his whole chase into history will be a MAJOR STORYLINE, likely with Flair involved in some supporting role, you know Cena wont randomly win #17 on a mid summer RAW, his whole chase will be played for all it's worth against the strongest champ possible for him to conquer, Cena and #17 sound like the main event to WrestleMania 32 to me if WWE decides to let it happen