Oh, I have partial answer to the original question in this thread as to why “Solidworks usually fillets easily”. I’ve been back and forth with Siemens support a fair bit over the export behavior in NX, and as I understand it, they roughly do this:
Fillets in Parasolid (the geometric kernel in NX/Solidworks) aren’t really Nurbs fillets until you export as STEP. What you see in the CAD software viewport while editing is their own secret sauce (note, not talking about the mesh here… they have their own “recipe” for the math as well). Basically, Parasolid remembers what you wanted to do for the fillet for each edge and shows you a representation of it, but the underlying traditional math never gets implemented (ie converted to B-spline surfaces) until the moment you export. And if you export a Parasolid native file, you get all surfaces except the fillets, for which only the parameters are included. Kinda neat!