Correct me if I'm wrong, but isn't GTO only valid for 2-player games - i.e. no Nash equlibria for 3 or more player games exist? If so, then "solving" poker by finding good enough approximation of GTO strategy only works for heads-up poker, which is a variant almost no one plays nowadays. Of course, in multiplayer games GTO is extremely useful where there's only two players left in the pot (you can view the remainder of the hand as a two player game and find GTO strategy for that game), but you still need a strategy for the remaining situations.