It’d be a lot of work to build a search engine anywhere near as good as the existing alternatives,

And yet Brave Search has done so. You got to have to come up with better excuses for Mozilla's failure here.

Also, Firefox is not “paid for by google”

Around 85% of the $450 million they get each year come from Google.

Who knows what skeletons are still hiding?

Go and have a look? https://github.com/brave/brave-browser

My argument is that Brave is a Chromium browser with questionable business goals, but it is also the most private and secure, open-source, mainstream* Chromium browser. These keywords cannot be said about Vivaldi, Ungoogled Chromium and many other projects unfortunately.

That said, I primarily use Vivaldi because of its customizability and added features, something Firefox seems to reduce with every new version.

• Not quite on Edge or Opera level, and no accurate data can be found due to the removal of unique user agent, but nonetheless I'd argue it is more popular than others of similar kind.

Given their crypto functionality uses a third party which has been found to skirt the legal system I’d be a lot more concerned about this integration even if I don’t intend to use it.

They offered a tenuous high yield lending program, that the SEC only jumped on after it collapsed from the FTX contagion. Litigation is pending afaik and depends on whether the program qualifies as a security, but the SEC has been losing ground in their optimistic claims of what they think qualifies as a security (outcome of Ripple lawsuit etc.).

Don't get me wrong, any such program is sketchy and I trust Gemini less for having offered it, but IMO it doesn't put them on the same tier as an exchange like FTX or make me think they would inject malware into software they have a connection with.

You've used onion links. Brave implemented unsecured onion protocol in thier Chromium browser.

Anything using Firefox as a base can run onion links with a simple add on because Tor is just Firefox. Vivaldi comes with onion support right out of the box, doesn't support hate and is malware free.

I use brave and think it's the best browser available, so I'm not arguing against it or anything, but technically it just supports use of the onion protocol, it does not provide the same full suite of protections that the tor browser does

As Brave says themselves:

For users who currently require leakproof privacy, we recommend using the Tor Browser, which provides much stronger and well-tested protection against websites or eavesdroppers using advanced techniques to uncover a true IP address.

https://brave.com/tor-tabs-beta/