Why do most people view Firefox hardening as better than Chromium/Ungoogled Chromium/Brave hardening?

From a privacy standpoint, the big selling point of Firefox for a lot of people is it's customisablility. I'm just wondering, is there any reason that a hardened and customised Chromium, Brave or Ungoogled Chromium can't be just as good as as a hardened Firefox?

Ps.
I know about the while manifest v3 situation, but Google hasn't implemented manifest v3 yet. Until Google implements it, disregard it for now

brave chromium firefox hardening people privacy