Arc is VC funded, and Brave has Brandon Eich's fingerprints all over it (and he sometimes posts here) so we would have to first start by defining what we want independent to mean here, first.

I would say Brave is not independent because it uses Chromium.

If it uses Chromium, it's hardly independent.

Did the title change since you asked, or what is claiming that they aren't? I don't see anything on the title, the README, or the website making the claim you want defended. It just says "a" truly independent web browser, that doesn't seemingly claim exclusivity to that status.

They both use chromium so they’re not independent of some technology decisions made by Google.

Whether that level of independence is important is up to you I guess?