Exactly. Air coming in , as it goes through a TBS with horizontal ridges is not going to decide to slow down and turn around and around at 90 degrees, as if air has a mind of its own. And what about all the air in the center of the bore, much less the air that ripples over the ridges of the screw design. It would just slow down air. Smooth walls are better for smooth air transitions. Its like would you put a air intake tube that was smooth or with ridges like a wash board.