I remember about 5 or 6 years ago, believing they could be the next Austin/Rock of sorts, for a different generation. In many ways they both over-achieved given WWE's typical protoype, and they both achieved their dreams. Obviously they didn't reach Austin/Rock levels, but I felt their popularity in general would serve them both well, and it obviously did.
Because of their size/look, they had to break more barriers than most. And even in the last 5 or 6 years, the industry has become so much more exposed than ever and WWE became much more orientated towards the Cena/Orton push, and a lot of fans didn't and still don't like it. For a long time the WWE didn't really understand the organic appeal that Punk or Bryan had for a large amount of people.
Natural popularity took it's course, Punk got to achieve 434 days and Bryan got to achieve winning WM30. Shame that time took its toll and we never got to see that dream Wrestlemania main event between Punk and Bryan. I do feel that if WWE had been quicker off the mark, we could have seen it. Then again, the fact that WWE were very slow off the mark with both of them probably only added to Punk and Bryan's popularity in the eyes of the fans.
At least we are left with great memories of them both individually, and some great work of theirs together, both in WWE and in various other promotions. They have a hefty back catalogue that I'm looking forward to going through.