This is how we normally import a step file into an Assembly:
Is there a smarter way to handle it?
Just clarifying some confusion. What you are doing seems fine. You might run "optimize" on the bodies and then save too.
Optimize is the command that might be holding up this feature getting into SE.
Developers and planners want you to get the surfaces and edges rectified post import and before you place the part into its assembly.
There have been complaints of such un-optimized parts not mating correctly due to faulty geometry conditions, although optimize can be built-in seamlessly into the import process at the cost of large import times.