The options chosen when the user created the STEP are not evident to recipient until after import. I always find this frustrating, because some models come through nicely, and others have hundreds of faults and gaps with many surface bodies and few if any solid bodies. I think the latter case comes from exporting with exterior faces only (where the software does a terrible job of determining this) instead of simplifying the internal and then exporting exterior whole solid bodies. If I could feedback to all component MFR’s, I’d urge them to dogfood their own export by reimporting it and seeing first-hand what garbage they have created.
All the same, I have imported STEPs of deeply nested subassemblies, but have never encountered a Sweep or any other Feature in my STEP imports. I agree this is odd, and have no good ideas about it. (Install ref 2018 SP5)
No kidding. I always request a Parasolid because it usually comes in cleaner. (Never underestimate someone’s ability to screw that up as well.) Just a week or two ago I spent 1.5 hours inside SE cleaning up a part from Kohler Engines. The only bright spot was the fact that SWX would have taken at least twice as long to do it.