The one thing people then to forget is although wwe is fake/scripted, those guys are athletes. Brock Lesnar is an athletic specimen who happens to have a amateur wrestling background.
Its like this take a guy like John Cena who is a beast in the weight room can bench 400-500 pounds. Now if he trained in mma he could be good. If some of these guys were not "wrestlers" and strictly focused on MMA they could be good.
Imagine If kurt angle or shelton benjamin never wrestler in the wwe and go into mma.