However, there does seem to be an outsized effort applied to defending this not-real thing. A leader who defies the petrodollar has a good chance of getting killed or kidnapped. In a way, the same principle makes any god real: he doesn't have to exist, as long as people who will beat up non-believers do.

Total USD reserve involved in that transaction is not zero. They have to already hold dollars to do the transaction at all, which means a benefit has already been provided to the US. The transaction doesn't change the US's position, but enabling the transaction to occur does.