It's not about who patrols the Strait of Hormuz. It's about who and what backs them up. If the Iranians decide to sink the frigates there (to do their blockade)

It's not about who patrols the Strait of Hormuz. It's about who and what backs them up. If the Iranians decide to sink the frigates there (to do their blockade) then they can expect a visit from a US carrier group. If there is no force that can be projected there then it becomes about who can move more stuff there. Seeing as that's literally next to Iran, Iran is going to win. Look at Crimea if you want an example of what can happen if there's no force that can back you up.