For disclosure, I'm not the recipient of significant abuse, but I fully believe that it happens and is a problem. I'm also #acutallyAutistic and in the middle of a period of burnout, so brain fog is a limiting factor for me at the moment. It's entirely possible that I'm just unable to think this through properly.
I'm wondering if the harassment problem is because there's no direct, tangible consequence on the perpetrators (users or servers) for being blocked? Blocking doesn't stop the blocked from talking amongst themselves, and to others who do not block them.
Blocking seems to be the equivalent of "if I can't see it, it doesn't exist". If that's your only recourse, then all you can do is gaslight *yourself*.
Perhaps some kind of reputation mechanism might work? I know this has been tried before and has its own flaws, but I don't know if there's a way to overcome them.