First off, your time period is all wrong, itachi isn't 60 years old. Second, you prove my point by mentioning hax. Third, if Shisui can put Kaguya under Koto, which I don't know if he could, but even then, it still means he can win, and might even be Superior to Kaguya do to that hax because he can just activate it by looking in her general direction, no strategy to get eye contact required, right? I mean, if I have hax that activates instantly no matter what, it doesn't matter what hax my opponent has if it takes time to hit me. 4. The gap in power isn't that great-- especially when Itachi was able to fight KCM Naruto, and Shisui was hailed for his speed. Itachi wasn't. Naruto was. Itachi wasn't. So, IMO, I take that to mean that Itachi's raw power and speed might not have increased-- but his skill and Genjutsu might have, if at all. Honestly, I just think Itachi was always just that good after he came of age. He peaked and plataued at Anbu, which isn't downplay or anything, I just personally think that Peak Itachi (which is to say Edo Itachi without the Edo.) 5. even still, it's an unquantifiable, unknown, possibly even non-existent boost.
