The people who don't understand why Punk is upset despite getting to hold the belt for 400+ days, and facing Taker and Rock....
It's not that he doesn't respect the Rock or Taker, or appreciate holding the title. But the only reason he held the title for so long is because the rock was adamant that the person he beat for the title be CM Punk, and Vince respected the Rock's wishes.
And for all but I think 3 or 4 of the 17ish PPVs that took place while Punk was champion, Punk was not in the main event. IIRC, 2 of the ones where he got the main event spot had Cena in the match as well.
And the only thing his title reign was used for in the end was to build up Rock vs. Cena. You don't waste a lengthy title reign like that on building up a feud or a wrestler (or a part timer!) that doesn't need any building.
Even when he's told he's the man and given the belt, he's held back. Even when given the opportunity to hold the title 400 days, he takes a back seat to Kane telling John Cena to Embrace the Hate.
It's insulting.
21 months after Punk aired his grievances on RAW and said that "The fact that Dwayne is going to headline Wrestlemania [XXVIII] next year and I'm not makes me sick," Punk was dropping the belt to Dwayne so that Dwayne and Cena could go on and headline Wrestlemania XXIX.... just like XXVIII.
Rewatch his promo, and listen to his grievances. Everything he said has come true. And the sad thing is, Vince seeme to bring every single thing and person he brought up into the main storylines... most often with Cena. Heyman and the notion of "Paul Heyman guys," Brock, Laurenitis, Steph/HHH, Rock/Cena.... it's been a damn checklist for the last 30 months of main event angles they've used.
He was constantly the highlight of shows in a sea of mediocrity in terms of promos and matches, and he had no issues hanging with the best promo workers and keeping his composure during it all, and he clearly outshone Grisham, Cole, Lawler, and everyone else in the company on commentary while he was injured, and he knew it, and everyone else knew it, yet he never got that 100% corporate backing, never got his time to shine.
Oh sure, he had a few big angles here and there, he even got a title reign or two.... which was completely buried because he dared ask why management demanded that one champion (That being Punk, champion on Smackdown) be more presentable in public while the other world champion gets to walk around in jorts and baseball caps (Cena, who was champion on RAW).
All the bullshit and ego stroking and hard work and adoration and the hottest promo since Austin 3:16 and they still just. Didn't. Care.