Hi Chase
You are right , the Scarp 2 is a symmetrical design , exactly the same as the single, but wider.

The DR is a three season hybrid design. That is : a fly with two walls of mesh hanging from the top.

The Scarps are convertible 2 wall tents. Not that different on the surface from the standard single cross hoop/end supported tent that is very popular in Europe.
When you look at the details, then the Scarps have a lot of nice refinements that (I think) make them effectively larger,easier to set up and more ventilated than some.
So the extra cost is mostly the extra fabric.
This would be an ideal tent for someone that wants one shelter only all year around. Get the extra poles and it will take a good amount of snow too.
When it is hot the sides open up completely and you can unzip the end too.
Bigger and heavier than the Rainbow but still lighter than most.
Unlike with the Rainbows all of the floor space is usable with the Scarps. (great for the very tall)
Franco