I don't have time to go through everything, but I expect Souji to be a winning high godlike, if not better. Honestly, his interp depends on a few key things.
1. Light and Darkness Immunity=ID immunity. If you take this away, forms of "Non-elemental ID" pose a significant threat- like those who see Fate Storm as ID would see him getting splattered. It furthermore raises the issue of people saying "Well, the instant death looks like X"- While Deadly Fingertips is dark (and I believe checks that resist), what's Expode? Eliminat? Arguments can be made, but it gets messier from there on. Admittedly, there is precedent for "Almighty ID" in game in the form of Ghastly Wail (Or whatever kills you when you're feared, 100%), so he may just be vulnerable to non-elemental ID.
2. The World Persona. Him having it is a significant boost, giving him a persona he can start in with AGI 30 something points above average, for the crucial Turn-one quickdraws. Being New Game+ only moves against it. With it he has a great slugfest persona and pseudo-initiative with an arguably strong base than Minato, because it's rooted in a concretely huge speed stat.
Other than that, he's a hell of a dueller. An overkill 2 or 3HKO using some combinations of Debilitate, Power Charge, and Hassou Tobi, utterly mocks limit fighters, and can wall entire fighters. He's not as vulnerable to non-lethal status due to Insta-Heal- Celes, for example, can't rely on invis+Berserk/Imp=win, if he's recovering when he gets turns. If you allow 1, he's High Godlike. 2 without 1, and he's more mid-godlike: a contender but not powerhouse. 1 and 2? Probably has under 10 matches he loses.