I work with vehicle models and just wanted to let you know I’m having the same issue. I’m importing a complex .stp model in datasmith and end up with around 18 million triangles in my scene. The framerate is at around 10fps.
If I import fbx files though and get to a similar geometry count the framerate in the same scene is around 70fps.
Looks like someone was dealing with a similar issue years ago: DataSmith import issues
The last bullet of the first post seems to be a similar issue.
I’m going to try putting all the datasmith geometry into a blueprint and see if that makes any impact, but I don’t have many ideas. In my experience, if you try to export datasmith geometry as fbx it will just crash Unreal, so that’s not an option either. The solution might just be to not use datasmith sadly.