Itachi has totsuka and yata, so since they are part of his susanoo it is better, invisible against any attack from sasuke and can instantly kill him with one touch, even if it touches his susanoo
Sasuke wouldn't lose he has more stamina than Itachi does, and you are forgetting that Sasuke can spam his EMS techs, while Itachi will be exhausted after using Tsuki. And Sasuke has already broken out of Itachi's strongest genjutsu before with 3Tomoe Sharingan. And Itachi can hardly keep his Susano'o up for long while Sasuke has kept his Susano'o up for a long period of time look at his battle with Danzo and the five kages he had his Susano'o up for most of the fight.