Forms is not Xamarin. It's a DSL in the form of a NuGet (aka npm/cpan) package developers can use to attempt to ignore the differences between the platforms.

It's kinda like swing. Great for throwing together a line of business application and getting xplat ui for free. It's possible to build a performant application with the framework but it abstracts subtle things that come back to hurt you. For example. Forms apps on Android is a single activity, always, period. Fragments are cycled in and out of this activity as navigation occurs. This introduces subtle annoyances related to memory usage as the entire app must be running vs thin slice. It transforms the lifecycle of Android into the UWP or iOS lifecycle.

Again this is Xamarin Forms. It is not Xamarin. It has its place but please don't confuse the product due to poor branding.