The main communities where I want to date are EA and EA-adjacent ones, though. It's not much of a concession if I can only be poly with outsiders I tend to not be interested in, and not with people from this well-selected, higher baseline compatibility population.

Being able to have the kind of valuable interpersonal connections that are good for me (i.e. poly relationships) is just more important to me than EA is. It's just one of my hobbies, and I'm not interested in subordinating my life to norms within them interfere with good parts of my life. EA does select for people who are unusually value-aligned with me along some axes, which is important to me romantically, but if it becomes less accepting of poly / more conventionally conservative, I'll be less aligned with the resulting community and will likely leave and focus on other interests.