Not true: Lemm.ee famously did not defederate from most instances including hexbear.net, and likewise take a look at how short the blocklist is on Lemmy.zip. And mander.xyz only blocks Threads and literally nothing else (at least, not at the entire instance level where it would show up in their blocklist).

Exploding-heads was defederated from almost everywhere, but also it imploded all on its own independently (tbf, after the waves of defederations).

Anyway, Lemm.ee was pretty huge - wasn’t it the #2 instance after lemmy.world? - and lemmy.zip is fairly large as well.