Importing STEP models directly one day would be wonderful …
But at the moment the management of CAD Surfaces is too basic in Blender to be able to manage them … It must be done by conversion into mesh.
At the moment it might be useful to convert your files in the 3dm Rhinoceros format models and import it by use this addon … but anyway it’s a bit cumbersome … to be honest I haven’t tried it and I don’t know what results you could get.