It really, really did not. GTK+ these days is superior to Qt in some critical areas, such as HiDPI support. Lots and lots of new applications and platforms are being written in GTK, consciously choosing it over Qt.
That is by no means an accurate statement. GTK's HiDPI support involves an integer scaling factor for the whole desktop, and that's it.
Qt/KDE on the other hand allows you to simply specify the size and dpi of your display and everything will scale accurately, aided by the fact that KDE uses SVG icons.
You're conflating a desktop environment and a graphics toolkit. KDE <-> GTK+ ~= apples <-> oranges.
Futhermore, no, GTK's HiDPI support does not in fact force a scaling factor for the whole desktop. You can turn it on app-by-app. The fact that whatever desktop you're using doesn't utilize this capability isn't GTK+'s fault, it's the desktop environment's fault.
Now having said this, you could be entirely correct that for the time being KDE offers a better HiDPI experience than a GTK+-based desktop, but again, that has really nothing to do with the toolkits themselves.