Sasuke...has good character development ....Hahaha, are you serious?
Yeah, he does. Sasuke is an incredibly dynamic character who's constantly reacting and developing over the course of the manga. Through his actions, you get an extremely complete "map" of what kind of person he is, and most impressively the internal logic that governs his actions becomes very plain to see, despite the manga almost never dropping inside his head and making his thoughts explicit like it does with many, many other characters.
That's like, Good Character Development 101. If you want to create someone who organically changes over the course of the story, Sasuke is a great example.
Then please explain to me why Naruto, who was constantly struggling to survive in a place where almost everyone despised his existence and would rather have him dead, didn't join defect at any moment and tried his damndest to prove himself, never went down the same road as Sauske.
I understand that despite appearances, you're not stupid, you just haven't read the manga in what is probably years, and when you were reading it, you weren't paying that much attention, so I'll try to help you out here. One of the main crux's of Naruto is highlighting the differences between Naruto and Sasuke and explaining why they took the paths they did, and why they ended up diametrically opposed. They're extremely similar people despite appearances (which is why they're naturally drawn to each other).
Naruto's a very canny guy: there's a good reason he acknowledges (and Sasuke later agrees, when he's more reasonable) that if some things had changed, their positions might have been reversed by the Kage Summit.
They start out with very different goals that both revolve around becoming stronger: Naruto wants to become Hokage (first to get the Village's acknowledgement, and later to protect it), and Sasuke wants to kill Itachi. Both those things can't be achieved by anything but improving as a shinobi. And they both rapidly, rapidly improve, but where Naruto (with significant difficulty) meets success after success (especially in Sasuke's eyes, since he's not there to see most of Naruto's failures, like getting nearly killed by Kabuto), Sasuke keeps getting kicked while he's down.
Which sends his self esteem (mind you, he was already subtly suicidal, so going farther down from that isn't exactly a good thing, lmao) plummeting below the fucking earth. As soon as he wakes up from his Second Tsukuyomi, he challenges Naruto to a duel on the hospital's rooftop, trying to gauge if his suspicion is correct: if the Dead Last in the academy really has become better than him in so short a time, even though Sasuke's ambition is dead serious, and Naruto's is patently ridiculous.
It's a mutual fight, and a way of showing respect, but Naruto completely misreads the situation, and acts like an arrogant asshole throughout it (as Part 1 Naruto usually does in what he perceives as normal social situations), completely confident that he'll win. This, combined with Itachi not noticing Sasuke at all in their last meeting (solely there to kidnap Naruto), just rubs dirt in the wound.
(what a little shit you were, Naruto)
What makes it worse is that Naruto constantly escalates the fight: first bringing out Shadow Clones, and then when Sasuke pops those with a fireball, a Rasengan, which forces Sasuke to escalate to the Chidori. And worst off all, when Kakashi interrupts them and they end up hitting two water towers with their jutsu:
Absolute proof in Sasuke's mind that Naruto's overtaken him, despite starting out much, much weaker, with a dumber dream and less natural talent. The Sound Four arrive soon afterwards and bully the fuck out of him, telling him that they were useless before they went to Orochimaru and he gave them their powers; that, combined with the influence of the Curse Seal, is what makes Sasuke decide that leaving and going to Orochimaru will make him strong enough to take on his brother, despite Kakashi's attempt to steer him away.
It's obviously an incredible difficult decision though, considering that it takes him nearly a month to leave.
Sasuke's breaking lasts through pretty much the entirety of Part 1, where constantly getting shit on ends up making him take rash, short-sighted actions to reach his goal quicker. We see the same thing happen to Naruto in Part 2, when he goes up against Nagato.
Nagato takes Jiraiya, Kakashi, Fukasaku, and Hinata from him, all while showing him just how weak he really is (sounds very similar to Sasuke, how strange. How especially strange it is that only after this does Naruto really claim to understand Part 2 Sasuke, and understand the consequences of trying to bring him back (it's not that strange)). How does Naruto react?
Whoops. Naruto comes within literal centimeters of tearing the Nine-Tails seal off, which would have killed him, destroyed Konoha, and then who knows, probably fucked off. The only reason he doesn't manage it is because his dad programmed a literal "Hug In Case Of Emergency" button into the seal (smart guy), and the only reason he's not still shattered afterwards is because Pain rewards his fulfillment of Jiraiya's ambitions with a village-wide resurrection. If Sasuke had had
one of those, never mind both, he certainly never would have gotten as crazy as he did by the Kage Summit.
So... that's why Naruto and Sasuke ended up traveling different (but rhyming) paths, despite their similar starting positions.
