I didn't start using Vivaldi because they support V2, I'm choosing to keep using Vivaldi because of their continued support of it.
I used to use Chrome for testing, but I've dropped it entirely now that ublock doesn't work.
If Vivaldi also drops support for proper ad blocking (I prefer ublock, but Vivaldi has their own blocker that doesn't use any addon framework, not V2 or V3), then I'll go elsewhere, but it sure as hell wouldn't be Firefox unless there was no other option (there are a precious few to even try, but I would try them all before going back to Firefox). And it would probably have to be a fork, in a desperate attempt at some amount of feature longevity.
Also, I don't give Google control over shit. You're making a ton of uninformed assumptions. My browser is a client to access content - nothing more - replaceable on a whim. I don't feel the need to interconnect every software, account, or hardware that comes my way. Those who do are trapped by their laziness and desire for convenience, and almost none of them have any idea what they've given up.