The question is, can an anarchist which doesn't accept any AES remain a member of hexbear for long, or do they get eventually punted for "sectarianism"?
You can be critical of AES when not on a Hexbear account. "Left-Unity" doesn't mean "all leftist ideas are valid," rather, it's about coalition building. Again, understanding Lenin's analysis of Imperialism is helpful, as both the Marxists and Anarchists on Hexbear see what Lenin outlines as "Imperialism" as the greatest enemy of all Leftist movements.
In fact, just how many anarchists who don't accept AES states do you actually have in good standing
Unsure, I'm not a mod nor an admin. I think it's self-evident when identifying as an Anarchist that AES isn't your ideal, Hexbear's Anarchists usually just see it as a dramatic improvement on Capitalism.
How many who don't believe in left-unity?
Not many, I imagine, otherwise they would be on a different instance most likely.
Defederation has it's own uses, yes, but that also ironically makes it more difficult to avoid trolls. When you defederate from an instance for X reason, only the more irrational users are going to create alts to attack. Defederation is often over-used.