I had a conversation on this just Friday, so weird that it's on /. a day later. As a KDE user and Qt developer (who uses Qt). The widget's-only Qt of old was solid. The QtQuick that KDE4 was based on didn't really fit. It's a transition that's still being made. Couple that with Aaron Siego, who I called out for making non-user-centric design decisions, was more intent on showing off what they *could* now do rather (plasmoid rotation? what's the use case?) than using QtQuick to better the UI. Couple that with some integration problems between the classical widget/Quick environments, it was not the best of all transitions.
Unfortunately, that transition is still going on today. It results in a paralysis of direction and focus. Qt used to, with widgets, have seamless theme management so that a KDE App would look native. Unfortunately, the QtQuick primitives that were initially released don't. The higher order QtQuick Controls, came later, and with not the best license or quality. Internally Qt has been pulled in many directions and a changed hands several times. Trolltech, Nokia, Digia and now the Qt Company.
That being said, I think we are there now, finally, 6 years later, to really do software transition to QtQuick. QtQuick 2 is amazing and up-coming Qt 5.8 will be that release which is the completion of the concept.The 5.6/5.7 that is out now is really great, 5.8 will be the last bit of polish.There are still some holes, there always will be, but QtQuick is something so new and different it took a while to figure out.
As a developer who uses Qt, and has been using Qt professionally since 2004, QtQuick makes it trivial to write applications. The next easiest was with PyQt.