AFAIK there is currently no chrome extension available that enables the downloading of YouTube videos that isn’t adware. Certainly non on the chrome store. As you already coded your own ad-blocker, do you think there is a chance for Brave to ever include its own media downloader that detects every media on a visited site, lists it and enables the user to select which of it he wants to download?
You would certainly not get in the google store with that if it included YouTube but maybe just implement it in the desktop version. Also, I think this would give you an additional edge that sets you apart from other browsers in functionality big time and would increase your browser-marketshare - especially as lots of add-ons seem to not work on Firefox Quantum anymore and frustrated users are looking for alternatives.