DoH bypasses the normal resolver, and gives control over resolution to the browser. Not a big deal if your browser is from Mozilla. A little more concerning if your browser is from google.
That's how it's done now, because browsers want to push the tech when nobody else has yet bothered; but it would make a lot more sense in the long term for DNS to stay an OS-level concern, so I would expect DoH to be implemented by the OS DNS resolvers.