Look, I could point you to the blogs and patch notes for Chromium and Firefox and you could read into it and make your own conclusions from it.
From my perspective as a solution architect that has worked for several mid to large size organizations, is that security is difficult to measure and constantly changing. When I evaluate what software to use I do it on the basis of how they've historically addressed security concerns, and where the organization that develops the software priorities lies. My opinion is that when it comes to security, Mozilla and Google are about the same when it comes to Firefox and Chromium.
I haven't looked into Brave much, so I can't comment there besides it's another organization that you have to trust so it's inherently more risky.
There's a big difference between winning a rigged election, and losing an election but staying in power anyway.