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)
There's been speculation for a long time that the real reason Google pays for that is to keep Mozilla afloat and stave off antitrust investigations related to Chrome.
That may have changed with other browsers coming out, although almost all of them are based on Chromium. Ianal, have no idea whether or not someone can be a "competitor" if they're using largely the same source.
If it's true that Google is mostly paying for antitrust avoidance and that something like Edge isn't a "competitor", Mozilla has substantial leverage. Mozilla just needs to be cheaper than an antitrust investigation and potential loss of that case. I would imagine that's not hard to do, that sounds expensive.
Mozilla has opposed Google many times, and is doing so again in the very link you are commenting on. Mozilla is not completely free from economic realities, but we are definitely not controlled by Google.
(Disclaimer: I'm working for Mozilla as an SRE.)