Again, all other things equal, RGBS over SCART and RGBHV over VGA from the Dreamcast will be indistinguishable.
What can you say about this guy’s comparison video where RGB SCART definitely looks worse than VGA? https://youtu.be/zosZPMWQ_ZQ?t=23m
Because, again, the Dreamcast does not support progressive scan over regular RGB SCART cables. When you see RGB SCART in Adam Koralik’s video, it’s SD 480i running through the Framemeister; and, when you see VGA via HDMI, which is using the Akura, it’s ED 480p. The RGB SCART footage is based on half the video data compared to the Akura footage.
I should probably clarify that the aftermarket/third-party SCART cables with toggle switches activate RGBHV/VGA mode on the console and have built-in sync combiner circuits that allow the cable to output 480p RGBS via SCART, whereas straight SCART cables (such as an official one) activate native RGBS mode, which, again, is limited to SD/15kHz video modes.
A more equal test of RGBS and RGBHV from the Dreamcast would be to hook up a Toro via VGA to the OSSC, and then flip between RGBS and RGBHV using the toggle switch between the SCART and VGA outputs.