Google is the dictator of what gets accepted into Chromium and what does not. That's how open source development works -- even if the code is available to everyone, its maintainers control its future.

Regardless of how Chromium is run [1] Brave is still in a position to make their browser work however they want. They can choose what Chromium features to enable, and take the code any direction they want.

[1] Your categorization doesn't match what I've seen. Microsoft has been driving substantial changes as Edge moves onto it.

More significantly, (as far as I know) there is not much open discussion about Chromium’s goals or roadmap. The reduction of Adblock blacklists in Chromium was announced, there wasn’t some public mailing list where a flame war began over it.