I had the misfortune of writing a complicated WPF app from scratch circa 2010-2011. Performance using the WPF widgets was terrible compared to HTML/Javascript/Blink; we ended throwing away most of the WPF code other than the main shell and a few dialogs, reimplementing the importantant stuff with immediate-mode Direct3D/Direct2D to get the necessary speed.

I recall wasting a lot of time staring at decompiled .NET bytecode trying to understand how to work around many problems with it, and it was clear from the decompiler output that WPF's architecture was awful...