Filter lists usually can and do get developed independently from specific content blockers. Just because uBlock and Adguard also develop filter lists, does not mean that the lists are in any way dependent on their blocker. These lists are just a representation of elements to block on a website in a specific format. Any content blocker can choose to support these formats. You don’t even need an extension to contribute to these lists. You can do that purely with the browser’s developer tools and knowledge about the filter list’s syntax. If you feel better doing that on FF with uBO, fine. The resulting filter list still benefits everyone who uses this list. I don’t think this is a sufficient argument against Brave.
That’s why I said good luck with that. I’m not against Brave here. I pointed out the dependence of Brave on uBO’s list, derived from the clarification about the blockers are comprised of the engine and filter lists (their own filter lists), so others won’t misunderstand that Brave does not use anything related to uBO under-the-hood.