The built-in screen sharing for MacOS (just called "Screen Sharing" and distinct from the "Remote Desktop Connection" program) is pretty good. I think it's just VNC though, so if you've not found that acceptable then yeah, probably not gonna work for you. An X client on iOS would be pretty cool and someone might go to the trouble of making it if mouse support were added. Let me stick a BSD in a closet somewhere and client in from my iPad Pro with native-feeling X.
