if whatever alternative platform he uses (which you proposed could be his own website) can’t facilitate a bunch of other creators moving over, then his effort is useless against the whole issue of Twitch
...no? It isn't. He doesn't have to support anyone else in order to not support Twitch.
Other than that, I would recommend checking out the Owncast directory to see how a federated streaming network can work. Or even look at the current state of podcasts and just apply that logic to streaming.
People don’t want to have to use 10 different platforms to follow the stuff they’re interested in. They want their one platform to show most of the content
The only reason that doesn't already exist is because Big Tech doesn't want it to. They could all turn on Federation and make that a reality tomorrow. Again, I refer you to The Owncast directory to see what that future could look like.
I fully agree, but it doesn’t help unless there’s enough content “somewhere else”
Once again, chicken and egg. There will never be content somewhere else until someone puts it there.
GOG doesn’t suck at all, and sees much smaller sales numbers than Steam
That's because they only have DRM-free content, which means they have ~1\1000th of Steam's library, if that.
Personally I don't buy from them because they don't support Linux/Proton, even though they totally could. So I have to choose between free games or a free OS.