exactly Gai is at the same level with Kakashi who only has one sharingan and cant even use it to full potential, plus kakashi doesnt have the body of an uchiha to be able to use the sharingan for long periods of time. now itachi can have his sharingan on all the time without to much strain on his body and also has the advantages of performing hand seals fast as hell. we also dont know if itachi uses sharingan to full potential, he can probably get even stronger, isnt that the point of that organization?