xamluser

In general, UWP apps that feel slow or somehow off are web apps. UWP XAML is really fast.

UWP XAML has pretty much surpassed WPF with the latest SDK. There are some things missing, but the new features outweigh that and the performance is significantly better since it's all C++ and sits on top of DirectComposition instead of milcore. Many of the things that were removed (like FindAncestor bindings and DataContext inheritance) were done so for perf reasons or because they were refundant.

I'd use it as the basis for Avalonia instead of WPF. If only to have x:Bind instead of {Binding}, which thanks to function bindings removes a lot of ViewModel boilerplate.

It's actually the exact opposite. Mindfulness and not wanting things.

You might want to look at the UWP version of XAML. It has really useful things like compiled bindings (x:Bind), calling functions as part of a binding with automatic change detection of the function params (x:Bind only), x:Phase for progressive enhancement during scrolling, StateTriggers, and Setters for visual states (consolidated VisualStateManager and Triggers).

Not to mention the interop with the amazing Windows.UI.Composition API's, which let you do expression animations, Direct2D effects, lighting, parallax, backdrop brushes (e.g., blur the content behind an element), etc.

WPF's version of XAML feels quite dated now.

Also, doing layout on the UI thread is a severe perf limitation that currently affects all versions of XAML. Consider having the UI framework just specify constraints and letting the compositor/render thread compute the absolute positions ;)