It is the reverse if anything. If you have the world's largest economy, chances are you need 100% of the world's other economies to sustain high growth, in that case, losing US hurts.
Venezuela is basically a psuedo red Argentina and are performing like it.
They can still sell to 1st, 3rd, 4th largest markets and so on. There is no excuse but local corruption. In fact when China was a small UK sized economy after ww2, they were under total embargo by the west and eventually just grew so much that the west dropped all its sanctions except military equipment - because it wasn't affordable for them.
A part of it has to be from taking a steaming dump on 50% of their population. There's a reason the moment Mao signed civil war ceasefire, he immediately set out to remove sexism at nearly any cost.
There's also other stuff they're doing that has no human reasonable explanation (such as buying western products instead of Chinese). But before complaining about not getting the US market, I'm suggesting they should first try to get all the women back into an equal workforce and on equal consumer rights, and see if that improves the economy?
Indeed Iran doesn't have the historical foundations of hegemony like China has. But they're also able to copy everyone else's homework as they're quite the latecomer. What I'm sadly seeing from Iran is that there's all these ideas out there, but they're not trying them. They're only concerned about bunkering up with weapons and behind these useless values which have only brought backwardsness to the region, and rely on Russia and China's overwhelming military and economic might to create an opening for Iran to seize regional control. But there is no vision about how this regional control will bring greatness to the population.
