Poor design can and does impact usability for a lot of users. If you care about the utility, you should care about e.g. wasted screen space with extraneous padding.

>you should care about e.g. wasted screen space with extraneous padding.

Where KDE is better than Gnome whose UI looks like its was designed for tablet use or 4K+ displays. So yeah, on that front I do care, which is why I prefer KDE.