I think my biggest issue with the Gimp is that it simply exists. If it didn’t exist there’d be a huge hole in the free software space and people would get together to build software to fill it. But of course there’s no guarantee that would actually produce something better.
Maybe the real problem with the Gimp is that it’s built to scratch an itch for its own developers who are used to its bizarre UIs and workflows. For all the people I’ve seen complaining about the Gimp over the years, none have stepped up to create an alternative. I think this is likely due to the intersection between visual arts people and software engineers being extremely small (and likely most working for Adobe already).