I just now realized that the TV also overscans on the 480p component output from my Xbox, something I missed in my initial tests. Now I see my TV does overscan most if not all 480p signals, while VGA 640×480 is rendered in full.
Is the signal from an Xbox meant to be overscanned anyway? In Ninja Gaiden and while in the menu, at the top right is a gap between the menu and the right side of the screen that looks unintended to be seen by the player, and would be hidden if the TV overscans. Maybe there is an upside to it in terms of only seeing what the developer intended you to see?
I’ve also realized Ninja Gaiden specifically feels bad when paired with typical HDTV input lag, and no external processor will fix that. Even if I achieve my TV’s lowest possible lag of 22ms, it doesn’t feel right in this game, so I’m probably just going to use my monitor with the OSSC (and maybe the mClassic) from the original Xbox. That will give me computer level responsiveness.