>So they become self-reinforcing cess pools of thought that (hopefully) gradually lose relevance.

You've referenced engagement first, but then, you've ignored about it in your conclusion. That is, as long as the inflow counters the outflow of participants, the situation will not improve or will even worsen - just as we've experienced in the last decade.

Inflow is partially bots and sockpuppets-- and their share probably goes up the more toxic the environment is.

Have you seen the truly awesome GPT3 authored navy seal copypasta?

Perhaps twitter will eventually be autonomous machines throwing vicious and brilliant insults at each other.

Bots are humans until advertisers decided they aren't.

So, like COVID, have FB and Twitter gone to equilibrium or are they still gaining traction?

People leaving is not necessarily a problem, if the new ones come faster. If you are small, you can grow exponentially even if literally all users left in a month. But this becomes a problem once you grow so large that there is nowhere to grow. Which is probably the case with Twitter -- everyone already heard of it, and everyone who was tempted to try it already did.

On Facebook, I think the only reasonable way to use it is to create groups and only debate within them. Also private messages, but only 1:1.