I don’t think federation implies endorsement or support. It’s more like “isn’t bad enough to cast out forever”.

PieFed has more of a spectrum of federation. There are trusted instances, normal instances, silenced instances and defederated instances. So it’s not a binary choice.

.ml trolls still see content created on the instance.

Yes that is a bummer. I have made a few attempts to limit federation based on what the poster has blocked but Lemmy is quite good at pulling in content that it previously didn’t receive, which works around it. More effort on this is needed.