You mean making a living off of someone else's content (with minimal commentary/editing), and getting upset when the owners decide that they don't want you using it?
i mean that you posting his content it's not the same of him playing a game (per se a transformative act,since he his playing an active part) and commenting on it.
if you make a video with his comment while commenting,criticizing it,then as long as you don't post the whole thing,it's fair use
but you have to play an active part..make the video your own
most of the "let's player" have their subscribers not thanks to the games (since most of them play the same games),but because of their personalities,their arguments etc..basically thanks to the active part of the video