Nah lemmy.ml didn’t slip under the radar, it’s intentionally still federated with because it’s the main instance of the core lemmy developers. Said developers also own and operate lemmygrad, but lemmy.ml is meant to be neutral ground.
lemmy.ml never really used to be that bad, either. It was only after the mass defederation of hexbear that users from there started making alt accounts in other instances, lemmy.ml being one of the main ones and, unfortunatley, lemm.ee getting its share also. lemmy.ml is still ostensibly neutral ground, however now it has a pack of refugee users skewing how its perceived.
I think feddit.uk is still federated with hexbear btw.