Don't get me wrong, I didn't say Trundle wasn't a good jungler or a good ganker. He just isn't what I would consider the "BEST" in terms of cream of the crop. He's up there but he lacks a closer move without using a summoner spell and he lacks a hard reliable CC. You need those two as abilities, not summoner spells, to be considered the best ganker type from the jungle. It guarantees that when you go for a gank you don't lose it. Trundle isn't a guaranteed gank because of that lack. Yah pillar DOES help with ganks, but it is hardly full proof. He does decent damage, but he's not the highest damage either of all the pre level 6 jungle viable chars either. This is the same reason I don't list Xin as one of the best gankers despite having a closing ability, a slow, and a hard CC with his knockup. His knockup is not reliable since it only works off the third hit. Which gives the person you are ganking a chance to retaliate with their own CC and/or get away. Xin does have high burst damage though at least. But it's not full proof ganking with even him.
Still he is damn good do to his speed, safety, innate tankiness, and good damage. That and his healing from his passive keeps him going strong. He is a great champ and works well late game as well. He can gank and gank well, but he is just not the best ganker out there.