It is an area that @sam is actively working on. It does seem that newer versions of Discourse have regressed in this area, performance-wise.
That being said, the real solution is to use a live chat tool if you need live real time interactions for hundreds of people at the same time – though I continue to question how and why chat is “useful” when it’s scrolling so fast nobody can really see any of it, ala Twitch and YouTube streams. 