For me, it still mostly comes down to usability. A big part of it is probably that I just have more experience with Photoshop, and if I really forced myself to use The GIMP more, it might grow on me... But when I am working in Photoshop I always feel incredibly productive, where as whenever I have to use The GIMP, I feel like the interface is constantly fighting against me, trying to keep me from getting my work done.

That's interesting because I feel the same but about Photoshop - having learned editing on Gimp. I'm curious to hear from someone who knows both well.

I used to use pirated PS as a teenager, and switched to Gimp later on. My experience has consistently been: for basic selection masking, color changes, and minor adjustments(i.e. things you would typically do to photos), they're equivalents. For graphic design, Gimp lacks in certain features that add flexibility; the text tool is not as robust, and there isn't a direct equivalent to effects layers. The UI of Gimp tends to have more "irritating adjustment" involved and forces more early commitment. And PS has a much deeper set of content creation options - especially so in the later versions, which I've read about but haven't used.

I'm interested in learning Krita next. Krita is more explicitly an creation app but it also bleeds into other spaces in its new versions as it accumulates more features. It's gained animation tools, and its interface more closely resembles the classic PS look. Krita has a lot of velocity which makes me think it may surpass Gimp as an all-rounder in time.

The digital tablet based art is still a better experience on photoshop rather than gimp (I admit I have tried this version but not recently), but there are also more mature alternatives to that end. Photoshop also has some better features for working with 3D files natively that I don't think gimp has tried to tackle.

At this point for me I am doing Krita for art and photo manipulation, and Inkscape for vector. Krita has really come a long way recently and works well on Windows as well as Linux. So far I have enjoyed working with many files at once in Krita and some of the live edit things (crop/selection sort of stuff) feels a bit nicer.

Content Aware Fill (and other such things) turn a 30 minute job in GIMP into a 5 minute job in Photoshop.

Granted it's not perfect, but it's usually good enough™

Also I find Photoshop's UI to be a lot prettier and more fun to use, even though I tried learning GIMP first.

Is that a UI issue with Resynthesizer/Heal selection, or are you comparing a "plugin-free" GIMP with Photoshop?