Isn't that a separate issue? It sounds like it is sufficient for the edits, but not for the task of working with other people who use / content made in Photoshop.
You're right that in some sense it is a separate issue. I could do my edits in GIMP some of the time. However, since I have to keep Photoshop installed for interoperability, there's no real reason to also install GIMP.
