systemd-resolved is a separate process (not PID 1) that just was written by the same authors as systemd-the-pid-1.
Then this DNS resolver could get the distribution and usage it deserves based on its own merits.
Of course, that's not going to happen, because the creators want systemd to be an OS by itself, with every buggy unreliable component standing as a monument to them only, and that means strong-arming in projects that could never compete with the existing working solutions on merits.
In contrast i can pass data between GNU core utils, BSD equivalent, busybox, toybox, and expect things to work. Because the way they communicate is documented and stable.
In contrast i can mix ls from GNU, grep from BSD, etc, just fine.