“They’re also not infallible, and benechilas kovod torasam, it is questionable to undermine the accepted minhag based on a psak from the gedolei hador of a generation preceding them.”
Don’t agree with you here. They’re from a different group. I don’t think Satmars should be expected to be fine with Reb Moshe’s definition of a mechitzah just because he was the “posek hador,” nor should Chassidim necessarily have to go like him in this case. Feels like kind of Litvish imperialism to say that everyone should have to follow our poskim just because there are more of us.
Again, I don’t know the heter for the 2022 all-of-Brooklyn eruv because their site very explicitly does not contain it. This does bother me, but not solely for the reason that they are paskening differently than Reb Moshe. The issue is that they aren’t really “pakening” at all. They just built the thing with no public justification.