Trundle lanes well against tanks, but he's still very susceptible to kiting and CC comps after the laning phase ends.
Personally, I just find him kind of frustrating to play. His E and ult are both very powerful, but the rest of his kit is so easy to play around.
I always feel like complete dead weight in team fights. Even most of the other split pushers (trynd, nasus, yorick) feel more impactful in team fights than trundle.
He's one of those old school bruisers. He's insanely strong at just slugging it out with people, but he can't force an engage, and no one is dumb enough anymore to try to fight trundle through his ult. So you get stuck split pushing and shredding stats.