Ublock origin is much better than a DNS level blocker. It can block lots of junk inside a page that doesn't come from a different server.
I use a combo of both and many custom filters but just DNS blocking isn't enough and work the rise of DoH and ads served on-domain it's only going to get worse.
The element zapper feature on Ublock origin is unusable on Firefox Android because you can't select on-page elements with the precision of a mouse.
DNS adblocking is not at all the same as browser level adblocking. Also setting your dns provider to adguard.com entrusts them to see what domains you visit, which you may or may not care about.