A great achievement even for a game which is relatively simplistic like a MOBA. Still waiting for AI to become competitive in Starcraft which i think is a much greater challenge.
An impossible to beat Starcraft AI is already doable without all this AI training. Just by controlling every individual unit seperatly in impossible to counter maneuvers far beyond any human actions per minute. You could basically get an AI to win every single time with a handful of zerglings in a few minutes this way. You could train an AI for 1 billion years a day to play pong or you could hardcode it to never miss…
On the other hand. Pong is simple with 1 rule. Starcraft, or in this case Dota, have multiple facets to win.
Plus, most SC players just gg out of the game when they know they've lost. I'd think that is a more apt use for AI. Like chess, see out X moves; if it's a lost cause; call it, and get to the queue faster for another game.