Ngl gimp never took off because it’s UX is terrible, plus it’s far from feature complete.
It’s like freecad in that regard, it exists, it’s foss, but it’s massively inferior to the paid options because UX is horrible and it breaks in weird ways.
Foss can be as good or better than non foss, just look at blender or Kicad, but these two aren’t it.
If you’re conflating UI and UX then I can’t do anything for you :P