Yeah, I can't co-sign this one I'm afraid, chief.
Kakashi has never used the 1st Gate in combat to our knowledge. Like, literally not even a single time. And bro was in situations where a 5x speed amp could've actually come in handy. Let's go over some examples, shall we?
- Against Kakuzu, he was faced with certain death against his combined Ninjutsu. Did he use the 1st Gate's 5x speed amp to save himself and Team 10? Nope, he was going to use Kamui, a move that was guaranteed to put him in the hospital for an extended period of time at that point in the story. To me, that math ain't mathing. If the Gate was a viable option or this standard part of his arsenal, then why would he choose Kamui over it when it's a move that simultaneously guaranteed to hospitalize him and not guaranteed to put Kakuzu down?
- Against Pain, we have a similar dilemma, except it's arguably worse. He chose Kamui once again over the 1st Gate even when it meant certain death. Like-
- Against MS Sasuke's Susano'o Arrow, he once again used Kamui to BFR the super fast attack instead of dodging using the 1st Gate's burst of speed. His stamina was a bit better at that point, and using a single Kamui didn't mean immediate immobilization, but it was still a very taxing move. Why use it if you have a less taxing option?
I mean, you get the idea. I can do this for practically every single Kakashi fight given the fact that he has never,
ever used it in combat.
This just empirically proves that, no matter how dire the situation or high the stakes may be, Kakashi simply just does
NOT resort to the 1st Gate in active combat. To say that it's out of character for him would be an understatement.
So with that in mind, I genuinely just don't see why Sasuke would consider it a factor when comparing Kakashi's overall combat ability to the Gokage's or his own.
It's also a total assumption that Sasuke even knows about it. To say with certainty that he knows about it requires us to assume that he had the Sharingan active when he was standing on top of the cliff waiting for Kakashi, which not only makes no logical sense, but also happens to be impossible to prove as far as I know.
As you know, the 1st Gate offers no real visual cues to clue Sasuke in that it's being used, and from his perspective it just looks like Kakashi almost falls, then composes himself and jumps up. Without the Sharingan, there's absolutely no way he could tell it was being used unless he's somehow privy to Kakashi's inner thoughts.
And beyond that instance, he'd have no other reason to know about it given that it's not some well-known part of Kakashi's arsenal, nor something that he ever saw him use in combat. To say otherwise would be a completely unsubstantiated claim.
Furthermore, even if I were to concede to the premise that Sasuke has this knowledge somehow AND is assuming that Kakashi would indeed use the 1st Gate here, I still think the premise falls flat.
A short burst of speed isn't really gonna be enough to defeat Momoshiki or Kinshiki, especially when Kakashi is so much weaker than them overall. Especially when Kakashi becomes tired, weakened, and possibly immobilized afterwards - making him more of a liability than anything.
Additionally, the Gokage can be holistically a better choice for the task at hand and/or "stronger" than Kakashi without needing to be superior to him in every single facet. They certainly don't need to be faster than a hypothetical amp he never uses in combat to in order to be better suited or superior combatants to him overall.
I'd also like to point out, as others already have, that Kakashi at that point was
retired. There's no logical reason for Kakashi to be chosen over the Gokage who are active Shinobi, regardless of whether or not they were superior to him. Especially when he doesn't have some anti-Otsutsuki Kryptonite that's guaranteed to help them win this battle. Hell, Sasuke picked Boruto over him and Sakura, despite the fact that they are 1000% stronger than this version of Boruto for the simple fact that Boruto was
A) an active Shinobi and
B) He had a strategic use for him in mind.
This to me proves that Sasuke was looking for the best options from a strategic point of view, especially given the fact that he could only take a limited number of people. Meaning he looked at the situation holistically, rather than 'oh these guys are the absolute best at every single thing ever'.
So, yeah, to me all of these reasons as well as the reasons others have brought up throughout this thread make me highly skeptical of scaling people to a value that's 45x higher than the highest calced feat in the verse based on the line of reasoning proposed in the OP.
It's not even a line of reasoning that would be universally applied, since we're not scaling every single character who's supposedly 'superior' to Kakashi 5x faster than him.
Now, as for the Uzuhiko portion of the OP, I haven't looked at that too deeply yet, and from what I can tell it hasn't been meaningfully discussed yet. So I'll just reserve my judgement on that for now.