I'm not much of a gamer but what you are describing doesn't seem to be relevant, for example there are simpler games where moving using numpad is perfectly usable and desired. There is not really anything specific you're designing for there, you just chose to make that type of game.

>the developers of GIMP didn't want to put into the work to make GIMP have good UX

From what I have heard from GIMP developers, this is not correct. There is plenty of desire to fix issues, the main issue is lack of contributors. Please help if that's what you're interested in.

You're talking about "getting away with the UX" but I'm also not sure what you're talking about there, GIMP is not a commercial product that is trying to get customers. It's an open source project driven by volunteers who improve it in their free time because they feel like it.