That's the thing about plot, it's contrived by nature.
A hypothetical has not plot, it has no aims of drama and tension to fulfill.
We understand the mechanics of Summoning. If Naruto accesses Kurama's chakra especially, he's not pulling out a tadpole. He's summoning the boss or something with a similar mass.
I can kind of agree to disagree on this one. I prefer looking at averages. If until the pain arc, Naruto ends up in more life threatening situations then not without being able to really use Gamabunta after the Gaara fight, it makes me feel like it's not really something he can rely on to win a fight, nor really part of his fundamental PL in Kishi or the characters minds, like it is in the later part of the series, or with Kiba and his dogs or whatever. But it's sort of an inconsistency, so I can understand why you might have a different perspective.
Sasuke's Cursed Seal evens them out to an extent, but I don't think you can account for his performance against Naruto using it without accounting for Naruto's lack of killing intent.
Naruto's heart was never in it to the extent that it allowed him to fight without restriction as Sasuke did, who punched a fucking hole through his chest.
Imagine if Naruto wasn't trying to subdue Sasuke. If he was as resolved to capture or kill as much as Sasuke was committing to his revenge.
Without restriction, escalation dominance was firmly on Naruto's side, that is to say, he could take to a level Sasuke couldn't withstand. A level involving Tailed Beast chakra and giant belligerent summons.
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I'd say they were both ultimately conflicted in the fight. Sure, Sasuke was willing to kill Naruto, as he demonstrated, but it's not like he wasn't really having his own internal issues about killing him and potentially ending up like Itachi(which is why he ended up sparring Naruto). Naruto himself using the rasengan was a move that according to Jiraiya and Kakashi, could have potentially killed Sasuke. We also see Naruto lose it emotionally, and give in to an unprecedented amount of nine tails chakra at the time, yelling to Sasuke that he would break every single bone in his body etc.... I can acknowledge that Sasuke gets a slight advantage here, but nothing crazy. Naruto was far from half assing it, this was pretty much the most serious he took any fight in part 1.
Sasuke's curse Mark stuff also seems like a pretty intentional way for Kishi to allow Sasuke to fight Naruto when he uses the nine tails chakra, at least early on before Naruto really gets in control of it. It's no coincidence they're usually getting these powerups right after eachother.
Naruto isn't intelligent in the conventional, academic sense. They thought he was damn near retarded for a reason. He was like a kid with ADHD everyone assumes to be stupid until they find themselves in the right circumstances.
I don't think any of the names you mentioned could match Naruto's feat of learning the Rasengan in a week. Forget attaining perfect Sage Mode.
Neither Kabuto nor Orochimaru saw the victory against Gaara, and neither are not the type of characters that would be able to recognise his genius given they themselves were conventional geniuses. Orochimaru was also obsessed with the Uchiha clan and Sharingan, not so much jinchuuriki. His fixation was on attaining Sasuke's body and Kekkai Genkai because it aligned with his ultimate goals.
One of the most consistent things about Naruto in the story is that he breaks people's preconceived notions of him. That includes every teacher he had. There's not a single mfer pre-skip that didn't underestimate Naruto, including the people on his side.
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1. I think there should be a clear distinction here though. Kabuto and Orochimaru don't think Naruto is some loser of the genin or similar to a kid with ADHD lol, like people in the academy or whatever think. They also both know about his heritage and connection to Minato,and the nine tails within him. They've seen he knows elite Jutsu like the shadow clone Jutsu, They know of his achievements and personally saw him fight Neji, while they most likely heard about him stopping Gaara(a pretty important asset of the sound/sand alliance). But in Orochimaru and Kabuto's minds, everyone in Konoha has essentially become weak and trash that they can kill for the lols, r(with the exception of Jiraiya and Hiruzen), but in his mind, Sasuke is still special. Imo, that is just direct portrayal, Sasuke catches the eyes of guys like Orochimaru and Kabuto so early on, and we can't just say it's because he was an Uchiha. Sasuke at this point in the story had:
Copied Lee's taijutu in a month
Gained some control over the curse mark
Copied Kakashi's famous Jutsu, Chidori, that helped make him a ninja legend.
Sasuke is clearly being built up as an exception among even the Uchiha, under only Itachi in part 1(based on Orochimarus perception, obviously the audience doesn't even know of any others in the clan at this point).
2. It's true that Orochimaru is underestimating Naruto, but most likely his potential for progress only. He factually couldn't do anything to them or even Kabuto before the Rasengan, which is when he starts taking him seriously. Given the fact that Orochimaru was going toe to toe with three tails Naruto in part 2, is he really completely wrong for thinking part 1 Naruto was trash?
3. Naruto is potentially a quicker learner then the likes of Kimmimaro and Haku, but it's kind of hard to say, given the fact that they don't even have the opportunity to learn Konoha Jutsu. I'm just basing my argument on the fact that they had portrayal above even the adults and strongest Shinobi of Konoha, with Kakashi saying Haku was an example of a "kid younger then Naruto, but stronger then him". Naruto as of part 1 falls short of some of these guys, but obviously he catches up by part 2, where he ends up the strongest ever or whatever.
To be fair, Sasuke wasn't fairing too great against a bunch of them. He also had critical, real time support against Danzo.
Considering what the Kage later showed against Madara, I don't think he was ready to clutch 1v1 just yet.
Fair enough, Sasuke does get plot protection as well in Ship as well, but when he's having almost all the top dogs of the verse trying to mess with him and surviving, I don't think Naruto was really the guy who could have killed him for most of part 2, though he probably could have killed him towards the end.