he used to be able to top/mid AND jungle and win every lane.
gragas is pretty decent jungle pick now, because his early gank pressure is insane. slow + stun is too much cc for level 1-5.
oh, and about your leblanc comment..
don't talk nonsense, gragas needed roughly 300 ap to Q R someone at lv 11 that wasn't building tank.
leblanc is a top pick because she requires actual SKILL to play, sure her w e q r may kill ONE squishy, but then she used all of her abilities to delete ONE target, meanwhile gragas essentially destroyed 3 out of 5 members with his q r.