While Chromium itself is a very solid platform, and correspondingly Chrome is a hard exploitation target, it’s quite easy to screw up a fork of it. Comodo Secure Browser was a chromium fork that was fixed to an old version of the renderer with known security issues and was built to disable the sandbox. It also added libraries that were compiled without ASLR that worsened security for every application that loaded them.

Chrome has an enormous security team behind it in addition to P0, so bounties on Chrome exploits are around $500k. FF bounties are a fifth of that, which is probably a portion of less security, and a portion of lower target market. Brave could be doing terrible things that without an audit would be unknown. Web3 code is pretty terrible on the whole, so adding that to a secure base may not be great…