It's not so hard to see why ex-professional wrestlers get a hard time. Putting aside the issue of the cheesiness of it, there is the fact that
a) Although professional wrestling is a physically demanding activity, it is much more like stunt work on a movie than combat sports
b) Most of the professional wrestlters are primarily or even exclusively gym monkeys, so their only oustanding physical attribute is large, clearly defined muscles. This doesn't even guarantee that they will be particularly strong.
You can see why people would have some doubts about the ability of a profesional wreslter to transition to a combat sport.