Brave beats Firefox on the EFF test because it randomises parts of its fingerprint, which the Tor project seems to reject as a strategy for anonymity [1].
I find the claim that Firefox is less privacy focused than Brave a bit questionable. Brave certainly seems to have good and probably better defaults in that regard, but remember that Firefox is basically developed in collaboration with the Tor project and as a result has various significant (mainly non-default) privacy features architected in such as first party isolation, containers, and Tor-project-approved fingerprint resistance. Easily-disabled telemetry seems like a small hassle compared to such concrete privacy features which do not exist elsewhere.
And for example with something like first party isolation, it is unclear whether Brave would even want or be able to to maintain such a patch set on top of Chromium when it requires quite deep integration with the browser engine.
There’s also the manifest v3 stuff which will presumably end up in Brave at some point.
[1] https://2019.www.torproject.org/projects/torbrowser/design/#...