I feel this. I remember spending ages trying to figure out how to remove the bar in doom modeline (yes eventually I realised I could just make it the same colour as the background...), only to discover that it was necessary to control the size of the modeline.

I imagine this stuff is really deep in the internals of Emacs, which is why people are less keen to touch it. But if we were in the mood to do that, I would like even more CSS-like features, such as the ability to configure each side of a box property independently