The US can be viewed in the same way as the whole of the EU. Think of NY State as Italy. Now add all those countries/states together…
The effect of later importation is a time delay in exponential growth. The epidemic spread is muted for the later countries/states due to earlier lockdown (in theory), but releasing all at the same time will not have the same effect everywhere. Sounds obvious when you say it. The net effect is a longer flatter peak in the epidemic. EU started within about three weeks of each other, probably from a common event (skiing holiday). The US may have had multiple importations or with country spread.
A one size fits all can’t be the answer though in a country that size. Possibly not in the U.K. either. Epidemics are stabilised to local extinction by movements across borders. Be it in a hospital (Ward to ward), a town (home to school), a county (commuting, goods distribution), a country or a continent.
The genie is out of the bottle.