S-video makes a difference, but it doesn’t seem to me that the OSSC provides any real benefit when chained to the RT2X. It often looks better in 2X + smoothing from the RT2X instead of the 2X line multiplier coming through the OSSC. I think the only reason to chain to the OSSC is for 5x mode with the NES.
I still question if the video is worse because of the VGA converter. If so, how much better would it look with the component box linked above? Would it be worth it to buy the component box or just stick to 2X mode with the RT2X?