This is not a bad analogy for global immigration policy. When migrants move from a poor country to a rich one, they typically make three to six times as much money as before.

If everyone who wanted to migrate 【were allowed】 to do so, the world would by one estimate be twice as rich.

Yet this vast gain cannot be realised, because most would-be migrants are forced to stay where they are. ⑤The door is locked, and voters in rich countries hold the key..

I'm wondering if it is better to replace the bold part with.had been allowed, considering it is the 3rd conditional. It's a situation that didn't happen in the past.

This is not a bad analogy for global immigration policy. When migrants move from a poor country to a rich one, they typically make three to six times as much money as before.

If everyone who wanted to migrate 【were allowed】 to do so, the world would by one estimate be twice as rich.

Yet this vast gain cannot be realised, because most would-be migrants are forced to stay where they are. ⑤The door is locked, and voters in rich countries hold the key..

I'm wondering if it is better to replace the bolded part with.had been allowed, considering it is the 3rd conditional. It's a situation that didn't happen in the past.