Let me put it this way.
A wrestler is not just defined by longevity but also by how good he was at the peak of his powers.
Trust me - no wrestler will every peak the heights Stone Cold Austin did during 1996-2001, not even Cena. He was untouchable and hence remains the gold standard! The Rock was up there but leaving the WWE in 2003 hurt his legacy IMO.
Triple H was good too and as you said got many things handed to him including his wife (lol), height, build etc. But I still give credit to him for making it count and performing at a high level. He also reinvented himself several times from being Paul Levesque to the Celebral Assasin to a joking prankster as part of D-generation X before becoming the Authority. Had the aura to become multiple time WWE/World Heavy Champion and remained at the top.
Same goes for Cena and to a lesser extent Randy Orton - both have become stale but worked hard and rose to the top.
Undertaker and Shawn Michaels also remain untouchable with regards to their legacy - that Wrestlemania streak will remain immortalized forever and HBK was technically one of the best wrestlers ever. He beat Cena clean in 2007 - when Cena was at his peak. Trust me not easy to do.
My favorite of course was CM Punk. Did not have longevity like the others but my god that guy had a peak like no other from 2011-14. He literally turned the WWE universe upside down during the Summer of Punk. Amazing presence and was technically as good as HBK if not better. I actually quit watching WWE when he left after Royal Rumble 2014.
Now going back to Jericho - granted he stood the test of time and had longevity going for him but was never at the top of his game. He was never THE GUY and although did have a few championship runs - he could not be at the very top for too long but was a solid midcard worker and, as you mentioned, did well to mentor younger talent. He was probably on par with the Big Show who like him got several pushes and championships throughout his career but could not enjoy a sustained run at the top.
Still a very good career by most standards but not ATG IMO.
I see where you're coming from but you see with Cena in particular, his peak has lasted a very long time; there are very few top guys ho can match his list of stellar performances in big time matches and how long he has managed to stay at the top; we have also seen him get over in a TV-14 era with the thugonomics gimmick and in the PG era which has been mostly restricted in terms of creative freedom which is why John has portrayed the same face character but despite that has managed to remain over with the fans. I'd say only Bruno Sammartino compares to him when it comes to longevity and performance. No denying that Rock and Austin were more popular but would they be able to get over in the same manner in a heavily scripted environment with little creative freedom?
The Rock just wasn't the same when he feuded with Cena upon his return after 7 years. Orton is criminally underrated, he was huge as the legend killer and as a member of evolution during the TV-14 era those runs were critically acclaimed, when the business went in a PG direction he'd adjust to become an apex predator who was out of his mind it was another great heel run for him.
HHH deserves credit no doubt but since we're putting a lot of emphasis on the influence of seniors and whether or not WWE push you it has to be said that he has been very lucky to express himself on every level and win as many championships as he did. Jericho has displayed as much versatility as HHH if not more in terms of all the heel and face personas, be it WCW LionHeart, Millenium Y2J Babyface, Comedic baby face in the early 2000's, Undisputed Heel, Champion, The CodeBreaker, The Comedic Gift of Jericho Gimmick , Ayotolla of Rock N Rolla , The Jealous Heel, Conspiracy Victim in WCW and the best in the world at what he does gimmick which is arguably his greatest persona and resulted in the greatest and most critically acclaimed feud in the 2000's vs Shawn Michaels in 2008.
You see Jericho had all these incredible runs and main-event feuds despite the little opportunities which were given to him, he got over the hard way and would most definitely have had a longer world title run as THE GUY were it not for backstage politics, but in the AE era title runs were not lengthy anyway! HHH longest reigns came in the Ruthless aggression era once Austin and Rock had left, in that period there was literally no one who had the chance to have a big reign like him because he'd run through the entire roster burial after burial

Jericho would then take a break because he'd get lost in the shuffle only to return better then ever.
Watch this in the late 90's Jericho would win HHH to win his first WWF title:
But the win was overturned due to the "fast count" and WWE don't count that win, but just listen to how crazy the fans went! or when he made his debut to cut arguably one of the greatest promos of all time. But just listening to how those fans in the Attitude era go nuts for Jericho just goes to show how big he was back then and how a little bit of influence could have pushed him even further in terms of championship wins and reigns because he had that it factor or else Vince would never have had him go over Austin and Rock in one night; that is a monumental achievement.
Going back to Cena, when it comes to top guys be it Austin, Rock or Hogan I've never seen any of these guys as seniors put over the youngsters as much as Cena has. This is another factor which is important for me, in terms of popularity Cena will never match Austin, Rock or Hogan but as a package he has surpassed them as the greatest pure "WWE" superstar of all time when it comes to his acheivements and how long he has been at the top. Personally I rank Austin above Hogan, Rock and Cena given how good he was in the ring, on the mic, the youngsters he put over and the good business he did but I won't argue with those who say Cena is the best and many in the business rate him as such given his longevity, in-ring performances, the business he does for the WWE and the youngsters he has put over.