In his eight years on top, Cena has never done that.
in fact, anyone who draws sizable momentum, has it curtailed by Cena getting involved,
in the last year alone:
Brock Lesners Monumental Comeback
Big Show's latest mean streak
AJ's mental state and Relationships
Dolph Zigglers selling and top quality matches
The Shield and their presence and destruction over the roster (Pending)
Cena did not burry them, and he never curtailed anyone of these wrestlers. They were simply not good enough.
Why couldn't Cena curtail CM punk? Yea because he is much much better than all the other names you've mentioned.
Punk actually became the longest reigning champ in modern era after his matches with john cena.
When these junior competitors get a chance to go face to face with the biggest face John cena they need to perform like Punk did, but they could not simply deliver. Cena does not make them look weak but they are weak thats why they look weak.
Now Let me tell you why cena never loses clean..
1- Wrestling is a kids show right now
2- Yes, Cena plays the role of a super hero. Did captain planet ever lost a battle with any of the monster he faced? NEVERrrrrrrrrrrrrr .
3- Kids believe in super heros
4- They need a strong character like John Cena
5- Do you get the theme of this show now? No? let me tell you..Good always overcome the evil in movies,dramas and WWE in the end
6- WWE will never sue you for now watching