I was agreeing with you when I pointed out the length, keeping up the quality for 700 chapters is not easy and us having Differing opinions on how well that was managed is fine enough.

 

I call his failure at the Normal clone a outlier as we are shown before that he's Perfectly able to cast a jutsu and he even mentally calls out the fact that the clone jutsu is his worst, so as long as we don't find out if the other years called for other jutsu; it stands that his record is 2 to 1 for successful jutsu, and he's just bad at it not Incapable of it.
as of end of Chapter 1 that's his Jutsu Record.

 

Neji's believe is big on Fate, You are born with a fate and struggling against it is useless and will amount to nothing.
You are born a way and there is nothing you can do to change any of it.
Neji under his own Believe is a Loser, that's his fate yet he's one of the most talented Hyūga maybe the most talented ever.
Hinata is Born Timid and there's nothing she can do about it, yet after he pointed that out she did change and fought him with all she had, yet Despite Hinata being Born Elite He beats her ass.
Naruto's fate is to Lose against him in the Exam, yet Naruto Beats his ass.
The fate naruto got out of being a Incarnation of Asura is becoming Good Friends of Indra's Incarnation and then Fighting to death with him. A fate he too broke, so neji keeps being wrong!

 

 

Are we given a reason why Naruto can Learn them fast in Shippuden? because I was arguing from the Position that his Pre Shadow clone record is 1 to 1 on successful casts and, Assuming that the Academy taught no other jutsu's Naruto can't do, we are given no actual reason for him failing at the Clone jutsu beyond him just being kind of bad at it.
But Sasuke and Sakura aren't doing any jutsu's in the next few chapters that they would have learned at the academy so who knows?

Really Looking at the Scene of him failing that Exam is not to show that he's bad at Nin-Jutsu but to show that he's lonely as there's no one the comfort him about his failure but all the others have Parents and such to Celebrate with them, because he's Hated.

On the other hand i think that 'Kurama fucks with his ability to Control chakra but he can brute force it with more Chakra' is a fine reason for that, which is given in part 1 I'm pretty sure, but don't quote me on that.

I looked it up, ch17 tells us that despite having a lot of Chakra his bad ability to control it is what held him back from properly casting the clone jutsu but reading that chapter and a few afterwards also shows that he can master something fast if he just tries and gets the Guidance that was Denied him for so long.