When the person who converted the scanned nordschleife from ac to rf2 says:
"Seeing the original road mesh, it's easy to see what are the top priorities with AC, and they are not physics, but visuals. The 22.8km track, had a total of 33k verts total. That's awfully low. So AC can spend more horsepower on the graphics than rF2, which simulates a lot more things than AC does. It's surprising tho how good the feedback is in AC considering the low resolution mesh."
To me is quite clear the person who converted the track used the visual mesh, which has way less than the mesh built on the laser scan. However yea, is possible the person who converted Spa didn't do the same as the person who converted nordschleife.
However when Gonzo said in this thread, on page 7: "To which platform has their spa being converted and how is the quality? Codemasters conversions in rf2 looked disappointing." To me it seemed like he was not happy with the conversion quality.