shippuden sasuke was never that cocky like his pts self nor would he hold back his power intentionally. this was all set up to make sasuke lose at all cost so that KB can escape for the plot to advance for the kage summit.
The only viable point that made sense and didn't come off as an excuse was the fatigue. I agree that the Itachi battle took the living energy out of him but this was his own fault.
Why engage a perfect jin that quickly?
Tobi is a good boy he would have given him time but Sasuke was impatient here. Hebi Sauce wasn't cocky because he was trying to complete his life long goal of killing his brother. If Sasuke never held back his own power then he would have won, still would've been a great battle. What I am trying to get at it's unfair to blame KB of Sasuke judgements. It wasn't a nerf either. It actually fits the plot pretty well, since he was fatigued no CM either he would have naturally not pulled out his MS because he was trying to save his energy.
This is the only 1 vs 1 battle that I disagree with the plot nerf, I like Sasuke but this is too much.
actually, now that i think about it. kishi downplays sasuke alot ever since mangekyou.
His cockiness arises after him awakening his Mangekyo but his fights were superb dude. Despite his arrogance at the 5 Kage Summit, he pulled out his Susanoo which was stronger than Gaara's absolute defense and Amaterasu would definitely helped Sasuke out lol.
Against Danzo he create an MS genjutsu to keep Danzo believing that his eyes were still open for Izanagi. That was pure brilliance from Sasuke. Kishi doesn't downplay him as much as you think he does.
Take off your biased glasses and then look bro.