The whole entire fight would be hypothetical, seeing as if Sasuke had either MS or EMS, Itachi wouldn't even be alive.
Hypothetically if both were to be at their prime, Itachi has KA, Izanami, Izanagi, Sakegari, Yata, Susanoo, Amaterasu, and Tsukuyomi, whereas Sasuke only really would have the less three, but at a much less grander scale. How wouldn't Itachi win?
Again, Sasuke would of died multiple times in his fight against Kabuto, while Itachi proved to be superior to Kabuto. That in itself says Itachi > EMS Sasuke.
Why do you think Kishi had to give him such a huge power up?