You couldn't be further from the truth. Have you seen the Blizzard app (Qt) [0]? The JetBrains Toolbox app(Qt) [1]?
Also, here's a small app I wrote in kotlin and swing for my GF who wanted to download music from youtube without installing crapware downloaders [2]. You'll notice it has a custom window frame, support for drag and drop, and fully customized table and buttons. I spent about 5 hours styling the UI, and half a weekend writing the entire app.
Yes, I agree, dowloading music from youtube is immoral and illegal, but I'm showcasing the UI so please ignore the underlying purpose of the app.
[0] http://l3.yimg.com/ny/api/res/1.2/v.xvnI7eUsLskyHopY6Kkg--/Y...
[1] https://www.jetbrains.com/help/img/idea/2017.2/rm_py_toolbox...