That’s because the crime of genocide tends to contain within it multiple instances of crimes against humanity, breaches of the Geneva convention, attacks against civilians and so on. It’s basically the ultimate crime containing all the other crimes within it. And the highest authority on international law in the World, the ICJ, has said that it is plausible that what Israel is doing amounts to a genocide. It really is very clear and simple, if you’re willing to see things as they are.
I agree, while the head of state is the more important and powerful position, the president certainly isn’t exactly powerless and handles the day to day business of government. But calling the leader the Ayatollah is slightly misleading. While it’s a requirement in the constitution that the head of state be an Ayatollah, Ayatollah itself is a religious rank, not a political one. So there are many Ayatollahs around, even more since the revolution as many believe that the rank has become somewhat inflated.