It's not about fads. Good UI is evergreen, even if it looks a little dated. GIMP UI is everbrown. You could dress it up in the latest colors and styles and it'll still be awful to use because the foundation is warped and misshapen.
I make drawings for posters sometimes with the aim to "look pro" for a local party. I am quite bad at it, but it looks ok. Like, do high level users have different needs?
I just fired GIMP up to see if I am missing something and I don't really see what.
That said, GIMP is lacking in two particular feature areas, its selection tools and its completely non-existent nondestructive editing tools. The transform tools are also a lot less wieldy, and GIMP's text tools, on top of being unwieldy again, have rendering glitches in their antialiasing code that gives everything a green tint on my machines. There's many pain points like that where things are lacking, more difficult to use, or subtly broken. Fine if you don't dive deep, but increasingly frustrating if you do.
Could you please elaborate? Is this about fast selection of complex and semi-transparent objects (e.g. hair)?
> have rendering glitches in their antialiasing code that gives everything a green tint on my machines
This is a Cairo issue though. See here and further: https://gitlab.gnome.org/GNOME/gimp/-/issues/8455#note_15219...
Regarding rendering, wherever the issue is in the stack, it's been over a decade and it's killing GIMP's usability for an extremely basic task, regardless of whose fault it is.