Italy 'banned' flights from China before we did. Obviously that didn't work. The virus was already here by that point. In any case, let's say restricting flights from China buys you more time. You have to actually do something with that additional time in order to get any benefits. We did nothing with the additional time. Didn't ramp up any tests, and we spent most of the time believing "it's just the flu"
Most of the Asian countries (South Korea, Taiwan, Singapore, Hong Kong, etc.) have done a phenomenal job with containing this virus. Western Europe and the US have done a terrible job. There's no way to sugarcoat it. What do those Asian countries have in common? They went through the SARS epidemic. In other words: They were prepared from the get-go and took it seriously. We didn't. In fact, South Korea and the US had their first COVID case at about the same time. But South Korea has done a much better job at containment.