You need to either KO, Sub or completely outclass the champ!!! Did GUS do any of them? 
JDS KO Cain in their first fight.
Cain out classed JDS in their second fight.
Serra TKO GSP in their first fight.
GSP outclassed and TKO Serra in their 2nd fight.
Weidman KO Silva.
Silva TKO Franklin.
That's how you take the belt!!!
Cutman - Frankie edgar vs BJ penn
https://www.youtube.com/watch?v=LBG3PplJ51w
Frankie did dominate BJ.
Forrest vs Rampage?
STOP WITH THIS