You can think for yourself. But to spell it out for you: if all countries had simultaneously shut down travel for a couple of months then we could have all been at the level of New Zealand or Japan. Neither of which crashed their economies. Once vaccines were available we would have been able to open up travel again and we'd have been better off collectively. Even those places where they did shut down, because after they opened up they were still exposed to plenty of people who imported the virus from abroad, something that would have happened at a much smaller scale otherwise.

So you can reason it out, the fact that we can't re-run the experiment is a pity.

> if all countries had simultaneously (...) Once vaccines were available (...) that would have happened (...)

You are piling up suppositions upon suppositions to come up with a wild claim. It doesn't work that way.

In case you doubt it, here's my equally plausible counter claim: if all the countries had simultaneously shut down, vaccine research would have taken the back burner, wouldn't have had sufficient funding, and mRNA vaccines would have never become mainstream. With the fake reassurance that it was a dud crisis, opening up to travel again would have caused a much worse human toll.

It's equally impossible to prove, but it's just as plausible, as it's extremely close to what happened in Australia - a country that was heralded as an example to follow!

> So you can reason it out, the fact that we can't re-run the experiment is a pity.

Indeed, but it's not a reason to throw logic out of the window. We just can't say what would have happened if everything had been wildly different.

We can just try to learn and improve for the next time on small details: most of the big countries managed to get a vaccine with their local industry, but some didn't. In some countries, the existing regulations initially prevented the rapid diffusion of tests, etc.

It's less ambitious, but more workable.