Manifest v3 itself is an improvement and is probably non-controversial. I can't see why anyone would think deprecating manifest v2 along with removing webRequest is a good thing. The latter is what everyone is mad about when they talk about "manifest v3". I'm not sure whether you're trying to making a nitpick point about the difference between the two, or you legitimately think the latter is a good thing.

Can you expand on the security improvements of v3? This is the first I've heard this.

As for performance... That sounds dubious. Declarative blocking surely will be faster than v2, but what is being blocked by v2, I would imagine, is generally way slower than the difference between v2 and v3. At the end of the day, I don't see the performance of my browser negatively impacted by uBlock Origin, I see it saving CPU, bandwidth, memory, privacy, etc.

I'd be willing to bet that whatever isn't blocked by v3 is sifnificantly slower than whatever supposed slowness there is with v2 (in general).

Google's PR has claimed that manifest v3 has security and privacy improvements, but it's pretty straightforwardly a lie.

V3 security is like closing a window in a room with fully open door --- it's good if we have someone watching the door , and we don't.