It depends. Are Brave's ads more similar to the banner ads of the old days? If they are not so intrusive and privacy violating like modern ad-networks, that would still be a net win in my opinion.
As for the hypothetical youtuber, they are always free to put product ads directly in their videos if they can/want to. However, if they can only make money via abusive 3rd party trackers, that's on them.
I've had Brave as my mobile browser since early 2017 and the only ads I've ever seen on it are the random Google Adsense ad that slipped through. These instances are in the single digits, in 2.5 years. im in Canada, so that might have an effect.
