The workflow beneath converts a LandXML to a directshape in Revit. I guess you can further develop this to solids and whatnot, but unnecessary in my context.
Notice the python script which uses regex in python to find all the names of the surfaces. Somehow this can also be done with the Clockwork regex nodes, but I'm not sure of the input syntax to those. Please notify me if you get it to work with the Lunchbox XML nodes or with Clockworks regex nodes! :)
And the result:
And here you can see the difference. Direct Shape on the left, Topography generated with Site Designer on the right. As you can see the result from site designer is unusable. I'm not familiar with the causes, but Revit topo tools are really bad when points have the same XY value in different heights, so I'm guessing it has something to do with that fact.
I haven't tested this 100% through and through, but I'll give you the link for the script (0.9.0) and let you take it for a spin. Please feel free to comment and maybe we can make the script better together! :)