At the platform level, you have to have a security model, and sometimes it will conflict with functionality. I’m sure there’s a lot of potentially interesting browser extensions you could build with the ability to read and write arbitrary files, but Chrome has decided (much less controversially) that the sandbox is key to their security model and extensions can’t ask to escape it.

If manifest V3 ad blockers were nonfunctional to the point of being broken, I’d be more concerned, but in my experience they’re perfectly OK.