I am so sorry for the negative initial experience you've had with RadSlideView. Straight to your questions:
1. HorizontalContentOptions and VerticalContentOptions are needed when the ItemsSource of SlideView contains strings or images, so the Views are auto-generated. In this case, there is no other way to define the layout.
Anyway, I agree with you that ContentOptions of the SlideView shouldn't override the LayoutOptions of the Views inside the control, I have logged this as a bug in our public portal, you could follow the item here:
This will be resolved in the next minor release of Telerik UI for Xamarin.
2. At this point we cannot update the default values of these properties, however, by fixing the issue referenced in pt.1, I assume we'll avoid the described situation.
I hope I could help. Let me know in case you have additional questions/issues.
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