This argument is flawed because 1) many streamers do exactly that, and 2) just because a streamer is not interesting when he's not playing a game doesn't mean that all the value is coming from the game. A juggler is not interesting without balls, does that mean it's the balls providing 90% of the value?
Given that:
* many streamers spend a substantial amount of their time just sitting and chatting with viewers, no game being played.
* if it was the game providing the value, you could just show a recorded playthrough without a streamer there to interact with the viewers, but this is not very popular.
* many streamers can play any game at all and draw a large viewership, but there are no games that any person can just start streaming and easily draw a large viewership
It seems fairly clear to me that the streamer contributes much more value to a livestream than the game being played.