“Professionals” is one of those words, you know, like “consumer” or whatever, that does a lot to hide what’s really going on. I’m a professional who used to use GIMP all the time for my work. I’m not less of a professional because I didn’t like Photoshop, in fact, I used to use PS at previous jobs but gave it up because I prefer the GIMP interface (yes, I’m that person) and didn’t need the other bits. “Professional” just means you do it as a job; it doesn’t indicate what that job is, and different people have different use cases.