"aping whatever the Windows equivalent looks like"
You may have missed that Photoshop is an Apple Mac application first...
And let's be sincere - most Linux UIs are bad and ugly. Even the widgets and fonts are ugly.
The lack of skilled UI designers and developers is very evident. It requires skills that go far beyond pure coding.
Apple first and Microsoft later have invested far more in UI design - although since Vista MS lost its tracks.
Anyway, being Photoshop the leading application with the larger market share, it's GIMP that needs to win Photoshop users, not vice versa.