I think what confuses the issue is the way that C4D and other poly modellers treat NGons.

If you create an NGon directly in C4D, the internal triangulation of that NGon is a bit arbitrary, particularly if it is non-coplanar. The smoothing algorithm then tries to smooth across those triangles, sometimes creating artefacts. Incidentally, the same thing can happen with non-coplanar quads.

However, when you IMPORT an NGon with vertex normals, each vertex has it's own normal, and the internal smoothing algorithm is turned off, resulting in artefact free rendering. In Modo this is even more evident. Where vertex normals exist, changing the smoothing angle for a mesh has no effect at all.

@flashfire - I'm not sure I understand your point about the models being "poly inefficient". The number of polys you use, whether manually or created by something like MOI, is dependent on how you want curved surfaces to look, and this is determined primarily by the angle at poly edges. The smoothing algorithm (Phong and others) can only cope effectively with small angles. Once you go above those angles, smoothing artifacts appear. Also additional edge loops are needed to cope with any transitions from curved to flat surfaces, which are not needed when vertex normals are present. Using sub-d with a low poly cage, is not the same thing as the sub-d is adding polys back in.