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.

This was true 20 years ago but has not been true for a decade. Blender evolved from among the worst UI/UX on the planet to among the best. It's now fast, intuitive, decently hierarchical and well-organized, leans into search and pie menus, in general it's very polished and in some ways ahead of the curve.

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