If you’re asking, means that you’re willing to go through arkenfox configuration, setting up your rules and parameters, etc… So I’d say go for it. You can always go back to LibreWolf.

Yes, I think that’s the point. Most browsers can be hardened, easily or not, but only few have actually good defaults.

That’s just browsers with default settings. Firefox doesn’t have a built in ad block, so it will always perform worse in that test. I guess FF + ublock origin + hardened settings (such as arkenfox) would perform like brave, if not better. For example, if you check android browsers, you see that Mull (a hardened fork of Firefox) performs great, even without ublock (that you can install as extension anyway).