People will use anything instead of gimp to be honest. Haven't tried it in a while but everytime I did in the past I can't help but question if it's developers actually use their own software.

Not me. Whenever I try alternatives, I can't help but question if people who use GIMP alternatives actually tried reading the GIMP manual.

If you need the manual it most probably means the UI needs improvement.

Only under the assumption they're designed for usage without the manual. I understand most things are but they definitely don't have to be. GIMP unfortunately may not be particularly explicit about this but having all users read the manual feels very much intended.