> Plus you can't share UI code between Android and iOS. You still need to build the UI's natively with no code reuse.

Utterly false - Xamarin Forms is totally cross-platform UI; you're probably mistaking it for Xamarin Native, which is used as a target renderer for each platform. Look at this sample project: https://github.com/xamarin/xamarin-forms-samples/tree/master...

The .iOS and .Android project folders target each platform respectively, with a single project shared between them that defines UI that is rendered onto each platform. You claim to have experience with using it, but obviously haven't done anything even as simple as a HelloWorld.