I personally prefer systemd and moved from Ubuntu to ArchLinux a long time ago in order to use it. But I agree with you, the constant overhaul of UI is a problem which is why I have stuck to Xfce for a long time. I however, do not use GIMP, but there may be other options out there.
By the way MacOS is Unix, it is a POSIX compliant OS. Also, you can run Linux on your Mac.
[1] http://without-systemd.org/wiki/index.php/Linux_distribution...