They do different things. Ad blockers help to manage things that are being displayed, but there are still off-domain scripts that are run that you don’t know what is buried in them. Plugins on website builder services, 3rd party data harvesters, god only knows what else. I use uBlock Origin in conjunction. Google Tag Manager is not blocked by uBlock. There are sites I’ve been to that had like 30 off-domain scripts trying to load shit even with uBlock active.