It’s available to everyone as a per-user setting, so it’d be good to let folks know about it.
Still, in your case, silencing and/or suspending the user is the right thing to do.
I think the way forward here is to for us to next get the silencing but fixed (we have it pretty high on our list already)
I think those mitigations should go along way, so that’s what we’d like to focus on first.
Beyond that, I think it’s worth considering having an option to disable @all or @here globally, or per-channel. But we haven’t made a decision on that quite yet.
There is also something on our list to ensure the existing max users notified per group mention applies in chat (it doesn’t currently). And maybe @all and @here should be subjected to the same limits.