Your description of the differences between Iraq and Iran is good, as well as your explanation of the current situation.
However, it would change significantly if the U.S. decided to stop half-assing it. If the douchebags running the show decide they want to commit to a full-scale invasion with all available assets, I think you'd see a situation more similar to Iraq. We could absolutely roll Iran's formal military if we committed to it.
But the subsequent occupation and attempt to maintain control would be doomed to the same failures as Iraq, Afghanistan, and all those before it, but on an even larger scale. All forward progress would stop once the Iranian military's command and control falls. There's no way we could win the asymmetric warfare that would follow, and I'm not at all saying we should even try. It's all a pointless pile of shit that never should have been started.