This would probably be the only viable answer. Dropping all traffic from a relay doesn't stop that same event from finding its way to another relay, and then to your client. You're sort of fighting the way nostr functions by doing that. I suspect it will be ultimately fruitless except by rejecting NIP-05 identities based on domain, something that some relays can already do themselves, and would be straightforward.
Discussion
I suppose they are all using mostr nip-5 verification.
That is correct. As part of the bridge bounty, bridged fediverse accounts were expected to have a NIP-05 identity at the bridge, to aid in controlling the flow of posts since, as we have seen, they can be torrential for users who only want to see a few accounts but not to be drowned in the flood on things like global feeds.
One thing to consider, though is a separate toggle for whether a relay appears in the global feed. The android client nostros does this and I rather like it. A natural extension to this would be to add individuals followed from that relay back into the list. You could easily do the exact same for the domain portion of a NIP-05 identity. More (sensible) toggles is better than shotgun style "mute the living shit out of everything" a la fediverse style blocklists and dns blackholing.
I believe this would facilitate mitigating clutter on such things, and still give users flexibility, rather than being constrained by the client they use
https://gist.github.com/fiatjaf/ea7d21e81359e1eb8abcb8805306adaa
The bounty, for reference
yep thats why nostr is so good, if the content is passed to anyone it likely cant be stopped