The Blender team did not always accept code or suggestions. This has been a running theme with several people I've known that felt their work and/or ideas were rejected by people that didn't grasp their brilliance. There was a possibly unusual willingness to say no, but it was more discerning than with GIMP which gave off the appearance of vetoing virtually everything. (At one time all GIMP woes would be solved by CinePaint aka "Film Gimp").
But it was combined with the idea of the studio, in order to find out where exactly the pain points are to be addressed. In a sense this is agile software done right, where you get the users and devs alongside each other with a common goal. Unsurprisingly one result is the UI today is not mocked in the way it was 20 years ago, while the GIMP UI has remained a constant point of confusion.
I'm not sure Blender development is "agile" in the traditional sense of the term because from the outside there are signs that it is slow paced with high inertia (specialists in charge of large features, planning over many months, purpose-specific contractors and GSoC projects, features that are delayed until they are ready), but they are certainly successful at delivering copious, high quality and high value features. Let's hope that the good leadership continues.
If only...
Competitively, libre office has a fairly similar UI to the pre-ribbon office suite, which people at the time much preferred once the ribbon came around (before they got used to it anyway) but it hasn't had the same disruption that blender did. I suspect the file format compatibility issues and die-hard Excel fans have a lot to do with it, but it's an interesting counterpoint to the assertion that the UI is responsible for the difference in adoption rates.
When the Ribbon UI came around in office, it faced a ton of push back due to moving so many things around and hiding so many common operations, but the file format translation issues between office and alternatives kept people in the MS cage, I think.
Nowadays many users grew up with the ribbon, so it doesn't seem so painful.
I grew up pre-ribbon. I did not like the ribbon. MS Office 97 still had a way better UI than anything open/libre office did.
If i had to rank, i would say
Old pre-ribbon ms office > ms office with ribbon > [a large gap] open/libre office.
Krita is awesome too and does interfaces right as well. Bought it on Steam. But I still use Gimp since the use cases are different. But it might perhaps be worthwhile to put your open source project on Steam anyway to make some bucks. I would happily buy more.
Blender did make huge jumps in recent years. Suddly you couldn't even update as fast as they introduced new things. It is amazing by now but I would argue that its functionality was unfairly derided in the past while it was already quite capable for quite some time.
Gimp for a looooong time was a multi-window user interface, completely antithetical to almost any other application released in the last 20 years or so.
Same as Mac software in the late 90s. GIMP is/allows MDI, tabs or whatever it is called. A decade old at least, Wikipedia is not clear if the change was "new feature" or "new default but avaliable before". Maybe Mac native software went that way too, no idea what is the trend there now. Most things reinvent everything including window management, poorly, inside a browser, anyway.
Gimp is an amazing tool and its creators deserve our gratitude. Then there is Krita, which is another amazing tool and its creators deserve our gratitude. Then there is LibreOffice, ditto. Then there is KiCAD, ditto. Then there is ...
I am not saying this to detract from Ton's contributions. I am saying this because a lot of people have made contributions to the open source world and, by extension, to the lives of many people. We shouldn't be treating this as a competition.