I agree, but I'd take it one step further actually. For me it doesn't cut it if the widgets just LOOK correct. I want them to BE correct. So, native widgets only please, no mimicking.
Not only that but if you reimplement the widgets then your always playing catch up when they change. It's better to just use the platform's 'primitive views' then constantly reinventing a wheel that looks similar. Someone else also mentioned accessibility which to me is a deal breaker if your app doesn't match a native apps accessibility.
Is there any such toolkit? What exactly is "platform's 'primitive views'"? Usually the "native" implementations are actually bindings to the native APIs which require heroic courage(a lot of manual tweaking), not to mention that you still need to catch up/update your bindings when these APIs change.
I would say that there is. Both Xamerian and React Native use the platforms Native views: UIView on iOS and View on Android. I agree that they are just bindings but that is easier then having to reimplement them as they all have small quirks especially when accessibility comes into play. I can't speak of Xamerian but I've written some of those Native bindings for React Native and would not call it requiring 'heroic courage'. It's actually quite easy and if you were on the Native side you'd have to make those changes anyway because those APIs changed.
WxWidgets are kind of that in C++ land at least. I know they use GTK on Linux and native widgets on Windows. They might not have good OSX support though.