Everything written in QML looks extremely out of place on the desktop, this is very much not an example of doing it well. You're right though that the infection has also reached KDE.

I wrote the block editor of my note-taking app[1] in QML, I hope this can show it's not QML that makes it a out of place - it's the care for aesthetics that developers put into the app. I also wrote a blog post on the subject if you're curious[2].

[1] https://get-notes.com

[2] https://rubymamistvalove.com/block-editor

Settings modules (KCMs) have been gradually rewritten in QML since a while ago, I think. Do they look "extremely out of place" to you? I personally couldn't spot them out. Efforts have been spent making QtQuick controls look the same as their QtWidgets counterparts.