I'm not entirely certain that it is systemd-resolved's fault that the distro maintainers are setting default servers in the config. I'm not disputing that RHEL might, but debian certainly does not, nor any of the distros I've used recently, but I probably have a completely different perspective as I have to deal with more end-user focused distros. I do feel your pain though, DNS config management seems to be incredibly hard. And this fuckery where a OS default setting overrides the DHCP config you're pushing would be incredibly painful.