 Well, yes, the presidency may be Iran's highest elected office, but you're right, it's definitely not the most powerful. The president does appoint ministers, ambassadors, he signs treaties, but it's the supreme leader, Ayatollah Ali Khamenei, who names military commanders, chief judges, members of the National Security Council, which the president nominally heads. The leader is also the one who picks the members of the Guardian Council itself. So the president really does operate in the shadow of the supreme leader.