This is just repeating a common meme. Blender's UI layout and organisation is fine, but this is a UI library. There's nothing wrong with blender's UI technically, in fact its pretty decent overall

Blender may be the single most polished open source project ever made.

It is actually a miracle that it is as good as it is considering other open source graphics programs like GIMP are horrendous to use.

There's a lot of thought in Blender's UI, and a lot of improvements over the years.

Fundamentally all 3d modelers have inherent degree of complexity. The ones that give a "simple" facade with fewer options make other things harder or having to look into obscure places.

All of that are beside the point however: people will use this as a GUI library, not as a Blender's UX design.

Can you give examples of what are polished UIs in your opinion?