Actually, in
overall feature set, Photoshop is still more powerful than GIMP. Especially important to the pros is a "true" CMYK painting space and colormatching so the limits of CMYK for a particular printer can be projected more accurately.
Still, for most users GIMP is plenty powerful enough.
Besides, most people know that with a search engine, Photoshop can be had for free, at only mninimal risk...