[boring_twenties]

That is absolutely correct. If everyone plays 100% GTO, then no one makes any money except the house. In order to actually profit, you need to deviate from the GTO strategy in order to exploit your opponent's mistakes.

[im3w1l]

Playing GTO against a poor player will make you money. This isn't the case in every game (rock paper scissor is the canonical example), but it is true in poker.

[boring_twenties]

Perhaps, but much less money than exploiting the poor player's many mistakes.