Well, in SR is quite balanced because the surface is so big that Teemo cannot cover it whole. Also, as big as the map is, he can't get to where his victim is as fast.

In TT, the area is so small and the passages so narrow that he can place shrooms in every turn and arrive swiftly. Its a matter of Shroom density more than anything. Even if you have oracles, Teemo has the whole map as an escape route, whereas in SR he has maybe 1 or 2. You can actually chase him.

I didn't think he was OP, but as time and games pass I realize it more and more. It's not just the map awareness. Its the whole map control thing.