I'm confused. Just tried the selection tool in GIMP and Krita on my PC and sketchbook on my tablet. Works the same way as far as I can tell. Just select, draw in there, copy/paste, ctrl-shift-a to unselect. Moving is more convenient in Krita and Sketchbook, true, but like that can't be it right? I'm at a loss.
That's because you know that "select none" is the correct tool to use in gimp most of the time. For lots of new users, "select all" seems like the more obvious option as opposed to "select none". The reasoning is something like "I want to be able to edit the entire picture, so I should select all". It doesn't help that "select all" has the simpler keyboard shortcut of the two. So they press "select all", then use a transformation tool like Scale or Rotate, and instead of simply transforming the layer like they would expect, it funnels them into the lovecraftian abomination of confusing UI design that is Floating Selection.
GIMP's layer system is definitely unique, sadly it hasn't much in common with the selection tool. In that sense, yes, it is unintuitive when migrating from other apps. I'd argue it's not that complicated, as gimp even highlights the buttons you should be pressing like a mobile game, but it is a complete non sequitur so back on topic...
If you use "select all" in any program to cancel selections, I don't know what to tell you. Like ok, GIMP is the jankiest of em all if you do that, no contest, but the rest doesn't behave correctly either if your expectation is that it'll work just like it did before you did any selecting. The flashing selection line around the whole page should be a pretty strong indicator of something being different.
Honestly, many GUI program, doesn't even have to be a raster art program; vector art like illustrator, 3D modeling like maya, some music programs, our custom spreadsheet stuff at work, even many file explorers, as far as I remember they all have the ctrl-shift-a shortcut and all would behave quite differently if you used ctrl-a excepting the same result. I'm genuinely at a loss where you'd get the idea to use ctrl-a to cancel a selection. Like I understand the intuition you proposed, but at what point do you just forget everything else you ever did on your computer?
Inkscape is a vector art program, it is fundamentally different to any raster art program. Like just download it and try to make just about anything with it, if you never used a vector art program, you'll be absolutely lost. If you know GIMP, Krita or Photoshop you at least have a basic understanding of the others.
I've played around with all four programs. I guess it just comes down to what you're using the tool for. I can't draw so I have no business in Krita. I've made logos in Inkscape and have used GIMP and Photoshop for different things. I'll start most projects GIMP and move to a more specialized tool of I need it.