Refactoring the hierarchy is a big and heavy task and unfortunately we have still some work to do. As you mention it is critical for you to declaratively define hierarchy children settings I would recommend to try the approach stated here
. Basically it is a hack to prevent the child grid in hierarchy to automatically build columns and settings and respect the XAML settings. Please have a look at the example in my post there. Meanwhile we are doing our best to push the improved hierarchy logic to a shippable state.
the Telerik team