It was and perhaps still is, a solid competitor to Photoshop, but any unfamiliar grownup is, quite reasonably, going to never ever ever trust anything to do serious work with a name like that.
As for CMYK support: why do designers even need to use this? Sure, not every RGB is the same, and it took some while before we even got sRGB as some standard, but the same goes for CMYK: every printer has its own profile. I had the displeasure of trying to get the CMYK profile of a "professional" printing company that only accepted files in CMYK, and they didn't even know which profile their printers used. Ideally you would send a RGB file including the display profile your screen uses, and then the printing facility converts that to whatever CMYK they need.
Of course there are also special colors or effects outside of RGB/CMYK that you might want to use when printing something, that's something else.
The discomfort, frustration and unintuitiveness you're feeling from using our app? It's just you!
No, that's not bad design and bad UX! its simply because we are different! We aren't X (Photoshop), we just do things differently here!".
GIMP is quintessential example of this.
We've implemented a number of items from the issue posts once consensus was reached, and we hope more people will participate and help improve GIMP further.
I believe Gimp could never enter the professional circles because it's internals are too tied to one, single colour model (RGB).
Professionals in many fields use tools with very bad UI/UX.
I use it semi-regularly and it does a great job for me, and most of UX is clear and obvious (high DPI support is lacking). But I haven't used Photoshop since the 90s (or Aldus PhotoStyler before it was acquired by Adobe ;)).
It really conveyed the image of cheap and shoddy. The drab looking logos, the name, and the weird looking poodle: all that just made it harder to take serious.
That "perhaps" is doing a whole lot of work in that sentence. GIMP has never, even now, been a serious competitor to Adobe's products for professionals. To suggest that if they simply had a better name they would be the top dog is laughable.
It's not about "me being personally offended."
It's about professionalism. It's a tradeoff. I see both sides of getting rid of e.g. "master;" but GIMP is so well beyond. Even if you make the argument that it's not offensive you're still stuck with a name that absolutely connotes "this thing is not going to be good at things."