Brave advocates should spend most of their energy going after Chrome and Safari users. If Brave can convert them better than Firefox can (which, sadly, seems to be quite a low bar), they'll overtake soon enough.
Attempting to convert Firefox users is not a long term strategy, and doesn't do as much or anything to create a better web.
I had been using Firefox for something like 15 years before I switched to Brave a few months ago. I was really skeptical of the crypto stuff Brave was doing and I still am, but at least they're innovating and trying different financing models. Meanwhile Firefox spent the last few years removing features that kept me using it over Chrome: rss, compact density, bookmark descriptions, etc. On top of that Mozilla gets 90% of their money from Google, and they still don't have a way to donate directly to Firefox, the only option is to donate to Mozilla and watch them spend most of the money on silly things like Pocket and other wasteful initiatives, while the people in charge just line their pockets.
20 years on FF here, I just switched recently for the exact same reasons as you. I got tired of their antics (not political, just goofy stuff like Pocket) and feature cuts. I tested every browser available, and came down to my preferences being Edge and Brave. Can't say I had an inkling of attraction to Vivaldi, Opera, or any of the rest.
I'm currently using Edge with uBlock Origin Lite. I can't tell the difference between uBO and uBOL. AdGuard MV3 also seems to work fine but I've used uBO so long that I'm sticking to it out of comfort.
That said, I keep Tor installed for as close to perfect privacy as possible. It feels academic though, as everything I do is pretty pedestrian and I generally avoid Google's services. I do prefer Edge to Brave, there's many features that I like here, but it's my backup plan if somehow Edge's adblocking doesn't work as well as it does today.
Even though I don't use it daily, I promote Brave to anyone that would normally be inclined to use Firefox. Otherwise, I push native browsers for all the inherent advantages they have. For me that's Safari on iOS and Edge on Windows. There's no doubt that built-in adblockers like Brave has is the future, they're just ahead of everyone in many ways. For me, Brave is what Firefox should be by now, in all regards.
Likewise. I loved Firefox and found their containers super useful. I've not been shy in sharing that their summer 2020 mobile rollout was so poor I moved away from it on both mobile and desktop (I often get flack from Firefox diehards for mentioning this though). Ah well. Chrome profiles for now, unfortunately.
I like Vivaldi on mobile with built in adblocking and some bit of control for text size (aging has not been kind to my eyes, mobile text is too small most of the time). Vivaldi hasn't made it pass evaluation stage on desktop for me as it often crashes when I try it (linux distros). (ed: tried it years before)
Browsers are going to continue to be a central part of our OS -- no stopping that. I hope the companies can be taken to task for colluding and that innovation is not stifled.
The last time I evaluated it in Fedora (maybe 3 years now?) it was crashing under moderate use, and haven't had time to check recently. Perhaps when some time clears up I should give it another go.
Attempting to convert Firefox users is not a long term strategy, and doesn't do as much or anything to create a better web.