Not saying it's perfect or better, just that we need it. we need a competing browser with a rendering engine that google doesn't ultimately control that has a non-trivial market share. Otherwise we may as well just stop complaining and let google do what it wants because we'll have no power to stop them anyway.
Quick googling confirms 50%+ of revenue came from Google 5-10 years ago, but couldn't find more recent data.
If Google is Mozilla's primary revenue source (especially if it's the majority), then Google effectively controls Mozilla via the leverage it has to pull Mozilla's largest revenue source.
Edit: Also raises the question, what company or organization should be developing browsers? A browser is something everyone expects to be free, but a browser is by no means free to develop, operate and maintain. For-profit browser companies (like Brave) would be forced to monetize the browser (like Brave tried to do with BAT crypto tokens, ads on the new tab page, etc)