The way that I see it, the issue with lemmy ml’s administration and moderation is not quite political in origin. It’s about transparency

Well it's really both. The issue is the combination of a number of factors which on their own would be fairly easy to deal with, but put together they are very problematic:

1. The admins are political extremists
2. lemmy.ml has a very prominent position in the lemmyverse, because they were first and got a headstart
3. The admins are actively using their position to heavily police discussion according to their extremist political views. The fact that they're not being transparent about it is aggravating, but not the root problem.

This prominent position of lemmy.ml is the fundamental difference with the hexbear or lemmygrad situation. Those instances can easily be contained at the user level: most people can just block and ignore them entirely because nothing interesting happens on those instances for non-extremists. Not so with lemmy.ml, which hosts a number of large bona-fide communities.

So I think it's necessary to make a concerted effort to reduce lemmy.ml's prominence in the fediverse, so that political extremists can't put their thumb on the scale to nudge discussion in a certain direction. Part of that effort is raising awareness about lemmy.ml's nature, which is what this PSA does, but that likely won't be enough due to network effect. It will take more to get people to move their communities to other instances. If other large instances, like lemmy.world, would block lemmy.ml that would provide a real stimulus for a large amount of people to move away from lemmy.ml.

With that out of the way, most of your suggestions boil down to “use lemmy.world instead”. I don’t have anything against LW’s administration, but I think that it’s foolish to concentrate people and activity there even further

I agree that spreading out more would be desirable, but on the other hand "just use lemmy.world instead of lemmy.ml" is a very simple and practical suggestion to move away from ml.