Yea, uBlock has kind of a line limit on how many rules it can use on Chromium based browsers.
But AdBlocking is not all, Brave still has telemetrie and so on (descr. in german blog https://www.kuketz-blog.de/brave-datensendeverhalten-desktop-version-browser-check-teil1/)
Vivaldi license doesn't allow changes and forks.
Ungoogled Chromium might be a better basis for Chromium based. Or Falkon (made by the KDE Community) with it's built in AdBlocker, but it's not as good as uBlock extensions.