Iran is a country and Hezbollah is at most a political entity. The comparison with Hezbollah was in the sense of dismantling the entire organization, which simply did not happen. Hezbollah still exists even with the elimination of its top leadership. Killing Khamenei would literally solve nothing. Israel preaches this doctrine of eliminating leadership, believing that it will change something, but it does not change much in strategic terms, because someone else always takes over and they cannot always count on a leadership that is more convenient for those who want a change of leadership.
Furthermore, even non-state organizations like Hamas, Hezbollah and others, with the elimination of their leaders, the organization still continues. What makes you think that if Khamenei were dead, Iran would fall? Someone else would take over Khamenei's power and continue the chain of command. There is nothing to suggest that Iran would be defeated if the top leadership were eliminated, the Russians don't even believe that, because they know that someone else takes their place, while Ukraine kills the Russian military leadership and someone else always takes their place and yet Ukraine continues to be defeated on the battlefield.