In my experience QT designer was awful to use. It’s probably fine if you are doing super vanilla layouts and widgets but as soon as my team started implementing custom css (or whatever the qt equivalent is called) things went off the rails. We pretty quickly abandoned to the tool completely to write the ui files by hand. They ended up much smaller and cleaner as a result. For some reason the designer seemed to add loads of unnecessary cruft.
So yea I can understand why they aren’t a priority.
That would seem odd.. the QSS is completely orthogonal to the code generated by the UI tool.
I accept that sometimes you need to some tricks with it and sometimes the layout in the preview is not the same you get at runtime which is annoying.
But in my UIs I use hundreds of widgets and I can't even begin to think about the useless effort required to write all the code by hand vs. spending seconds to drag and drop widgets into their place visually in the GUI editor...