Google has billions and billions of dollars to throw at Chromium; I doubt Brave has anywhere near that kind of money. The longer it stays fully forked from core Chromium, the harder it's going to be to pull in updates, and the more expensive it will be to maintain.
There is a reason I stopped using Chrome-based browsers years ago. Killing V2 was never anything but a play to make sure people see ads under the guise of “security”. While there is some security benefit, the main benefit is making sure Google is the only one spying on user’s every move.
This is what you get when people trust their browser development to a monopolist instead of a consortium. You get fast and shiny bells and whistles with support for the latest whatsis, but you also get this.