Sasuke manifested his full power with full intention to kill Naruto; latter didn't manifest his full power and made it clear he didn't want to kill Sasuke. So whether Sasuke said ''I admit, I Lost'' or not, it doesn't change the fact Sasuke was vastly inferior to Naruto at that point, hence he incorporated the 9 Biju's Chakra to Susanoo to fight on equal grounds with Naruto, and still couldn't bring him down. If the scenario was different and Naruto actually went with full intent to kill Sasuke, he would have done it low difficulty and in 5 sec. The power gap between them was too enormous. Naruto was just in a whole different league than Sasuke. Look at the difference in their fight against Obito, Madara and Kaguya; Naruto was the central force.