Sorry but you're full of it. Hate to break it to you but that's how all UI libraries work by definition! On Windows there is no standard widget set that everyone uses, an no agreement on how a widget should behave. Every framework has their own. MFC, WinForms, whatever MS Office uses, Wordperfect, etc. They all have their own ideas of what a widget looks like and does. MS Office has traditionally shipped it's own widget set with every release. Buttons, scroll bars, dialog boxes, the works. All of these uis use the Windows Theming API to give them common bitmaps to draw, and Qt is no different. Thus a Qt app absolutely looks and acts as good as any other widget toolkit on Windows.
On Mac also, Qt uses the Cocoa native apis to draw widgets, and then tries very hard to follow Mac standards to make them act natural, and to a very large extent they succeed. True on Mac people's idea of fidelity is at a very high standard, or so I've been led to believe.
Maybe your experiences have solely been on Mac where the fidelity wasn't as good in the past. I can tell your experiences with Qt were not on Windows, though.
On linux, of course, well Qt does its own thing, unless you have it use Gtk themes, where it does a very good job of looking and acting like my other Gtk apps.
In short you are definitely wrong about Qt. If you're right about Qt, then Winforms, MFC, MS Office are all just as unacceptable as Qt, as far as look and feel goes. There is no other way to do cross-platform ui toolkits. Don't even mention wxWidgets, because wxWidgets just thunks through to yet another toolkit, though it's provided by Microsoft on Windows so you would probably argue it is the one true widget set, even though precious few applications use it these days.