What's the point of preserving EA as a movement if EA can't direct people to work on the most important problem that it has identified?

The fact that you don't personally have a completely independent position on AI is part of why it's so important for serious organizations who have actually done this kind of thinking to very clearly emphasize how central the issues with AI are. Yes, they are extraordinary claims, AND there's a giant community of people who have substantially converged on the importance of AI.

Of course, doing anything comes with a large opportunity cost. The point isn't to notice that there's a large opportunity cost. The point is to try to find the thing that has the lowest opportunity cost. 

I hear you that things can end up sounding sci-fi. Where do you first start objecting to the story in AI 2027, for example?

I think this is a very bad take. AI is overwhelmingly more important than the other stuff. It's good for 80k to focus on it heavily or exclusively. 

If your point is "I disagree that AI is important", then write that post and make that argument. Don't write a drive by critique of people doing excellent work and doing it even more excellently by focusing on the things that matter most. That's the whole point, after all.