GSP did many disciplines before doing any wrestling. But his game plan relies heavy on wrestling.
It doesn't though, it depends on who he is fighting. Against Shields and Koscheck II, both full 5 round fights, 50 minutes of fighting, how much time was spent on the ground? In Shields I think it was literally zero, against Koscheck maybe a couple minutes. That is more than three full fights (3 round fights) where GSP did nothing but strike.
His gameplan is simply do whatever his opponent is worst at and he happens to have the wrestling to pull that off if that is their weakness. I really wouldn't call him a wrestler as a base.