does the fediverse actually support the kind of block that's being asked for here?
Yea, that's where I'm thinking the hangup on this might be. A block could be implemented, but it'd come with the caveat of that all it's doing is giving you the idea they aren't continuing to engage with you on your instance. On their instance, and any instance that federates with them, they and others will continue to see the replies.
Personally, I would like to see block renamed to mute to be more accurate and a block from replying added with the note about the drawbacks of them being able to tell you blocked them and their posts still going out everywhere else. That at least empowers the user to make the decision themselves on what they're most ok with. My reasoning is: changing the UI for, let's say an aggressor, gives them a reason to retaliate. To me, either blocking method is a lose-lose; either it doesn't stop engagement which some users clearly want it to, or it makes it obvious someone is being blocked which start aggressors down the retaliation path. That's kind of why I'd want users to make their own risk assessment on actions.
Anyways, that's all very unlikely to happen. Most of all I'd like the bug about notifications fixed because that is clearly not working as intended.