Whenever UI/UX is brought up, GIMP inevitably enters the discussion.
I've used it a number of times and do not find it any harder than any other piece of software — doing complex operations where you are not sure what you want to do (or especially, how is that called) is hard, but that's hard in an IDE as well.
I do not do much, but I do not do little with it either — I am perfectly happy with layers, selection tools, simple painting tools and the rudimentary colour correction I may want to do. And one can claim that the hamburger-menu-like approach started with Gimp, fwiw (right click on your image to get to a full menu, though you still had that menu at the top of your image window).
Two things have always been a requirement for proper Gimp use: "virtual desktops" — a dedicated one for Gimp — and IMO, "sloppy focus" (window under the pointer gets the focus right away), but I've been using those since at least 2001 or something when I first saw them on Sun workstations, so I probably never had trouble with extra clicks required to focus between toolbars and other dialogs.
For creating original artwork, I find any graphical approach too limiting — I _do_ want an easy approach of UIs, but I frequently think in terms of proportions and spatial relationships when drawing ("I want this to be roughly twice the size of this other thing and to the left") — I always try to imagine this combined tool that would fit my workflow, but then I remember that I am probably an outlier: I may have been spoiled having done mathematical drawings as a primary schooler in Metafont and later Metapost (for colour, or rather, grayscale :)), and being a developer since 7th grade, where it's hard for you to come to grips with how suboptimal doing precise drawings in any software is (I've done some minor uni work in AutoCAD too).