But then again, their design language has recently started to be less cohesive too (or more precisely, mix of older and newer design systems are apparent).
Like, it's generally difficult to get something working/looking nicely and consistently on Linux. A somewhat exception to this rule is GNOME, but even then there's issues with KDE/Qt app theming sometimes.
Like, until 2021 (I think) I lived with a broken looking inkscape and Krita (used it as a hobby) because I gave up trying to figure out how to fix the theming, since none of the fixes suggested online worked. Then one day after some random update it started working
So, there's a lot of space for improvement and better cross compatibility between these "subsystems"
Granted, though, it's getting better. But I assume not at a pace an average user can perceive. So, i thinking that's where people get frustrated.