You're really distorting the facts. Cain's list of early opponents was embarrassing to the extreme.
Also, Cain was dropped twice by Kongo. Cain is not a KO artist. He's not even close. Where do you get such an impression? He's a ground n pounder. He KO'ed Nogueira, but Nogueira's strategy is to get dropped every fight and pull you into guard.
Nogueira has worse defense than Jenna Jameson's...nvm
Carwin does have tremendous power.
Okay I will give you that, Cain is not a ko artist but a ground and pounder. But I think the point I made about Brock being a lot more scared of Cain and Carwins stand up game than any previous oppoent is a valid reason he may have looked different on his feet.