Naruto should be tired. He hasn't slept in weeks. Yes, he should have passed out a couple days ago.
However, Sasuke really doesn't have an excuse. He slept for the first day of the war. Once he woke up, he did a little sparring against a couple White Zetsu. Watched his brother genjutsu Kabuto. Then he went on a little trip to his old Village with a group of friends. After finally showing up at the battlefield, Naruto and the Shinobi Alliance had already been pushed to their limits.
Sasuke ran around a little since arriving, but Naruto and the Hokage have been doing most of the work. Even during their battle against Madara and Kaguya, Naruto did most of the work. Sasuke pulled out his sword and did a quick Transformation, but he has been conserving energy for his battle against Naruto.
This was the only way to even out Naruto and Sasuke's power levels. Going into the War Arc, Naruto essentially could solo Sasuke with his pinky finger. However, Kishi has since worn Naruto out and removed some of his abilities. At the same time, he gave Sasuke a major power up. Now their battle should be much more even.