> neither can tell you if your game is actually fun

I think this is the core insight. An AI will not be able to experience a game (or anything else for that matter) remotely in the same way that a human can experience it. It might be able to guess, based on human rankings of other similar games. But AI will never be able to actually have fun playing your game.

This concept will define the workforce that comes out of this AI boom. Maybe an AI can write a document or code like a human, only based on past samples of similar behavior, but it won't be able to synthesize exactly what it means to be a human. The human element will still need to be traded on. Your value as a human cannot be replaced, you might just have to think differently about that value.