For the second question, I guess this is beyond the scope of this discussion. Having communities unlinked to an instance would require a complete rework of Lemmy, this thread is just about moving away from lemmy.ml due to some abuse reported in the other thread.
On my side I feel like most of https://lemmy.ml/communities are already covered. This post is for communities that other people have already identified as "not having alternatives" (see complaints on the other post), so they should know them already.
LW is already much more active than lemmy.ml (18k monthly active users vs 2.5k: https://fedidb.org/software/lemmy/), so the system is working, people have left for a less politically biased instance
The Lemmy devs have expressed several times that they don't want to interfere on how people use their software (e.g. admin the instances and mod the communities).
Which is good (and allow us to say that they can't indeed interfere with Lemmy as a whole), but that also means that they won't be the one "cracking down on bad actors"
https://gui.fediseer.com/ might be something along those lines, with a chain of trust between instances
To be honest I might have forgotten to ping you actually (maybe because you were less active for a bit and I basically mentioned people when I saw their posts in All?) but at least now it is solved!
Are those services available today?