It's time for mass-migration to Firefox. Only losing users is going to tell Google that this is a horrible solution to enforce.
Is v3 an horrible solution or the deprecation of v2 in 2023? I ported one of my extensions to v3 and while the process was not completely trivial it did not took more than a few hours, in my opinion the change is worth it this makes extensions more secure. As far as I know Firefox is also moving to v3, maybe not enforcing it for now, but they will probably deprecate v2 at some point.
v2 also already differs in some ways in which Firefox thinks it makes sense. I'm not scared at all that they're gonna deprecate webRequest.BlockingResponse in favour of declarativeNetRequest, which is the specific API function that adblockers rely on. After all, that function has nothing to do with security, best you could argue is that it's related to performance due to filter lists becoming absurdly long.