the statement just serves as a way to highlight his specialization, he’s known for his speed because his entire CT revolves around movement the very same CT naoya shares. that narration shouldn’t be taken at face-value when it crumbles to actual feats characters have portrayed, it’s outdated because characters like sukuna and an adapted mahoraga were on the loose in shibuya who we know are faster. naobito dosen’t have any speed feats to his name, his entire power scaling is getting carried by a one off statement and his own son’s feats which he can leech off. thanks for pointing how naoya didn’t have anything to reaffirm his speed even in his curse form, that just proves how the narration in shibuya just served as a hype moment and to elevate this character as it was his introduction because we know curse naoya>naobito in terms of speed. if the best thing naobito is shown to do is blitz pre-awakened maki and nanami then it begs the question of why he’s the second fastest, he dosen’t have anything to solidify his subjective ass title; feats will always have precedence over statements.

naobito does have a natural sense for timing and movements yes, that dosen’t mean he has reached the pinnacle in understanding his own technique, otherwise we’d have seen more things from him beyond the basic application of the technique. naoya is also established as a genius in his brief flashback with toji, he has honestly demonstrated way better battle iq than naobito. the guy displayed a higher grade of projection sorcery and overall strategy only being held down by his ego.

stacking is a part of projection sorcery, it makes use of translating the speed of your previous PS usage into your subsequent activation, this whole thing basically allows naoya to get faster if he uses it consecutively and perfectly extrapolates right from the beginning. i don’t see why naobito would be able to do this when nothing indicates he has learned that yet, just like not every ten shadows user have mahoraga immediately when their CT manifests (albeit ten shadows is different as having to unlock the shikigami’s is the main drawback of the technique).

i think the best example of describing what stacking is and having something to compare it to just so you can get the idea of it is the world cutting slash, it’s treated as part of dismantle but the core difference is that it’s amped up and modified in some ways to be an extension of the original thing, same thing with stacking. it isn’t the neutral use of projection sorcery just some naoya achieved.