The difference is experience. Experience I speak from, haven made the move to WPF long ago...
WPF is not dead, but absolutely incompatible with anything you knew about GUI libraries
How do you come to that conclusion? Also wrong, there is nothing stopping me from using other libraries like metro, but why bother when you can design it from WPF's designer?
WinForms is a way simpler, FASTER
If you were to be challenged to write an application which draws some moving shaded squares, and bouncing balls, we would see who would experience poor performance, and I assure you it won't be WPF. Paying attention to the scaling problem you have in your video where the panels at the top are forced to redraw, and it cuts a whole square into your UI, as the panels are disposed of/repainted. This is only one aspect of the poor performance you experience with Winforms, compared to WPF.
Look of your app mostly depends from libraries
The look of your app should really be depending on performance, and not a stylised library, which stresses the performance of an interface which wasn't designed for such usage. The difference is that I don't need a GUI library to do what you done in winforms. I can already do that from within WPF. But you too would know that if you had the experience I do in making WPF apps.
The only part I agree with what you said, is the same as what John said above. There is a dramatically different environment to how code must be written in WPF compared to Winforms, and what code you previously wrote for Winforms, will most likely not be compatible in WPF, which forces you to go on the steep learning curve. As you said :
absolutely incompatible with anything you knew about GUI libraries
That's actually incorrect. The only thing that makes it different is how the code you have for Winforms, can't be used in the same way as most people expect on WPF, and here is where people get turned off the idea of learning WPF, and refuse to go on that learning curve, and instead stick to what they know instead. It is not only my opinion, but my experience, that makes me believe WPF is better all round. And with the addition of xaml makes for designing a breeze. Stick to what you know, or learn the advantages WPF offers before criticising it on the basis of what you think you know about it.
Edit, fixed 200 typos