I really dislike Curse for gaming, the UI is the most unintuitive thing I've used in ages, showing me the same information on 5 different looking screens, but not having a single screen that shows me a list of all of my friends. I don't use any of their addons as well because I don't want to bundle myself into a glorified chat app that can't even handle that correctly. I've had to restart not only curse, but my entire machine multiple times in order to get it to register a microphone switch or a switch in playback devices.

I agree with your main point of steam's slow movement, but the other thing is that steam is a very large incumbent with pretty high switching costs. I don't see them going away because a different platform offers twitch integration, because I can already stream twitch with my steam library that has hundreds of games in it. And if twitch limited that somehow, I think the pull of the user's library would overpower the pull of one individual streaming platform. It costs a lot more to switch the library after all.