Yea I can believe that.
I think that's the whole reason Sasuke's upgrades at the end didn't really match Naruto's in quantity after that point. People downplayed the significance, but Naruto wasn't joking when he said Sasuke was way stronger than him. He already had the most powerful chakra around and the hatred to maximize his power via the hatred-feeding sharingan.
He just needed stable eyes. Itachi-eyed Sasuke would've wrecked Naruto in a fight. SM is too limited. It took Danzo like 10 eyes to last as long as he did. Naruto could only use about two clones at best. And against Pain, he went tailed beast before he could finish the job with SM only. Sasuke can subdue Kurama. No help there. I got people on the base who can vouch I'm a Naruto fan. This is just facts.
Think about it. Not only was Naruto not physically strong enough to handle Sasuke, he wasn't metaphorically either. He went through A LOT of different personal transformations, you know the confronting hatred and his convictions thing, after that. He was tested at every level before they both finally got the Sage's powers.