The oldest GIMP gripe I've consistently heard relates to CMYK. If you're rendering things for digital use, that doesn't matter.
In the past year, I've needed CMYK for printing the box, label, and manual of a video game cartridge. (Yes, companies are still making new NES games on cartridge.)
Does Photoshop have features and UI that GIMP lacks? Of course! Do you need them? Can you even name any of them[^1]?
GIMP has been improving so fast that some GNU/Linux distributions haven't been able to keep up. GIMP 3, released in March 2025, added nondestructive adjustment layers like Photoshop. Ubuntu LTS still has GIMP 2 and is expected to get GIMP 3 in third quarter 2026, though that isn't a problem for Flatpak or Windows users.