You think wrong totally
RGB SCART is the best picture quality
Normal AV is lower quality [Yellow video] (It's not vastly lower by the way)
Both are fine for NTSC display, but SCART is the only one that will auto fix the display on an older PAL only TV set giving you a colour NTSC signal at 60Hz, Normal AV on a PAL only set will either give a black a white image @ 60Hz or will just have a scrambled B/W image @ 60Hz
The problem has nothing to do with the video cable used
I play NTSC games all the time on my PAL PSone/Saturn/PS2 all via RGB scart, I have also done this with my Dreamcast (I use VGA now), My GameCube (I use my Wii instead now via VGA) my Xbox (I use component now though)
I don't have this issue.
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