"Iran has not gone "head-to-head" with the US. The US has the military capability to level Iran if it chose to fully unleash it."
Sure. We could nuke the ---- out of Iran, but we could do that to any country.
The US could have, um succeeded, but that would first require a theory of victory. A set of objectives. From there, you would determine how to achieve those objectives. Normally, you do that by holding something your adversary values at risk. In Iran, I would say that would most likely be the coastal areas, ports, and oil production facilities.
That never happened. OEF has been the biggest strategic defeat in the history of the United States. I have no idea what objectives the DoW established prior to the conflict, but unless the objective was to burn through thousands of critical munitions, those objectives have not been achieved. And unless the US is willing to deploy a massive ground force, the Iranian victory will stand. More cruise missiles will not do anything to change Iran's decision calculus. They've already won.
Germany and Japan should go ahead and claim victory in WWII.
Technically, there were no losers in WWII. All countries came out stronger than they had been.