Topography is Revit's ugly duckling.
It's already pretty bad when you only have New Construction, but when the Existing phase comes into play it gets really bad.
The Graded Region essentially replaces the entire Existing phase with a New Construction copy and Existing is the Demolished in the New Construction phase. So on your demolition plan your entire topography is simply demolished, regardless of what you actually want to see changed.
Applying surface patterns to the parts that actually have to be demolished can't be done except with per view Filled Regions. Unbelievable!
Building Pads are oblivious to phase so you have to use workarounds for that too.
All the while Autodesk representatives tell us we shouldn't expect to see improvements to Topography. They seem to think you should master Civil 3D if you want to make plans with groundwork. As if that is going to make your Revit plans correct.
Easily the worst part of the Revit Architectural experience.