I don't understand how that would prevent the US from sanctioning those banks and companies that trades with Iran? Regardless if they traded through the described mechanism.
The reality is that we are 16t worth of trade and Iran is 440b. They're just not worth it.
Which really obviates the only real reason to have the EU - combined, all the EU countries are stronger in any field than the US (or China).
That being said the US is a basket case. Sure bully the EU. It’ll work today, maybe ten years from now.
But the US is a failing concern, with a completely rotten and corrupt ruling class that lead ppl to vote for an oversized Twinkee for president. World wide hegemony is done in twenty years.