I think GIMP is still pretty important because it at least gave you options over buying or pirating Photoshop. Nowadays, I use Affinity Photo over any of them, but the importance of choice matters, because piracy doesn't impact Adobe's reach. It further entrenches it as the norm.

Today, with Krita, Affinity, Pixelmator and the like, I would never suggest its "morally right" to pirate Photoshop, because you will still inadvertently support an Adobe monoculture. The morally right choice is to use anything else, and the competitors are functionally capable of supporting 95% of Photoshop's features.

Also, GIMP did give us GTK, which solved a very real issue with open source desktops -- none of them were actually open source at the time. Gnome still conducts the very important work of supporting GTK.