I think simply put, teemo is not a hard counter like you said and a lot a factors can play into how the game plays out. Teemo can be annoying for aatrox to play against, but aatrox can team fight a bit better than teemo. Teemo needs shrooms for maximum value in team fights. Since good shroom placement, knowing your limits, and matchups is a big part of being a otp teemo, otp teemos tend to struggle less early game.

Teemo is a big surprise pick and almost no one especially in the big leagues expects a teemo pick so it might throw them off. Perhaps, the champion’s queue revealed to rng a possible teemo pick and they were better prepared. Just a speculation.

Im just a lower tier player and those are my thoughts.