That's was Sasuke's strongest Jutsu as he said, Naruto's strongest jutsus shown was his super tailed beast RasenShuriken that contained each element of the Bijuus. Sasuke focused all of the Bijuus chakra into that attack which was more than what Naruto did, Naruto formed 2 FRS attacks instead of forming it all into 1 attack so Naruto's attack stopped Sasuke's stronger one. Mind you, had Naruto been 100% at the start then his attacks would have overwhelmed Sasuke's. Sasuke used a ton of chakra before this fight as well, he needed the Bijuus chakra for more as Naruto needed Natural energy. Both at 100% puts Naruto above Sasuke in power and stamina.