I've only hacked on GIMP a small bit, so I'm no means an authority, but the sad truth is that GIMP is an extremely small project driven mostly by volunteers. There is a desire to correct these issues but there are many, many other issues to prioritize them against. It's been a very infrequent occurrence for them to have the resources to work with UI/UX designers. I'm not trying to dismiss your complaints, but I think you would see some better results if you didn't wait for someone else to fix it for you. My only suggestion is that GIMP actually has very complete Python/Scheme scripting interfaces that can be used to make a lot of little UI tweaks, although the APIs are not well-documented.

>they do things their way, not the way users want or are already familiar with

In my experience, a program that has never had a feature removed (or unintentionally broken) is an exception, not the rule. It takes a lot of effort to keep things working over the years, and if there is no will to maintain that, then those things will disappear.