Being ‘extended’ 1) assumes we know when it will be over (we don’t yet!), and 2) we can calculate when/if we are through it, and when/if we would have been through it.
It would have required massive, and likely unsuccessful mobilization to lock down travel (both foreign and domestic) enough to actually control Covid aka New Zealand. Considering the land borders and smuggling problems there alone, I think it would have been ultimately futile.
Considering how politically fragmented the country was and still is even before the pandemic, trying it somewhat successfully may also have kicked off a Civil war - not that anyone would have tried that hard.
Vaccination rollouts could definitely have gone smoother, and better programs to manage the rollouts would have also been really nice - but given the situation above, it would only have been a (short) while before Delta or something like it got going anyway and started spreading.
Fewer would have died from COVID probably, but overall deaths may have been similar (more violence during riots? More shooting and civil unrest), and the fear and other issues (socio political strife for instance) would still have happened, just looked different probably. These types of situations are brutally hard.
Overall, I’d give the US a solid ‘C’ grade. Not great, not terrible.