I understand completely. GIMP has never been very good (though quite usable in many cases). GTK (Gimp ToolKit) is a nice library, though. Krita is much better, but is very focused on painting.
At least you can run a real OS whenever you aren't using that specific software. Any reasonable linux distro will use <10gb including all the software you really use, and have a nice automated installer to shrink your windows/mac partition and install in the empty space.
Sure it's not ideal to have to reboot, but with solid state drives, rebooting isn't very much hassle anymore.
Before anyone even starts — GIMP is not viable in enterprise workflows.