It worked in China and Vietnam, neither of which are small or island countries.
As for your edit according to which this is only possible in large countries if they are totalitarian, the tactics China used are exactly the same that NZ has used, and are fully consititutional in the United States. Basically, telling people not to leave their homes for two weeks, using the Army to deliver food and supplies, and stopping travel between cities. These tactics have been implemented historically in the US in other epidemics and pandemics, so unless your claim is that the US is authoritarian, I don't follow.
China has totalitarian control over its populace which can simulate the level of control possible in a small island democracy. Vietnam I haven't studied.
It is fully constitutional in the US to stop travel and enforce quarantine in cities, and has been done before, and this was only ever needed in a select few cities in China.
Here in Canada I'm not allowed for the next 28 days to socialize with anyone outside of work. This is more restrictive than what was imposed on most cities in China.
You can't nail people's door shut in the US with them inside, which happened in Wuhan. You also can't unilaterally and swiftly implement extreme lockdown measures that would be required, only China can move that quickly with its one party dictatorship. So it's not a valid comparison being made here.
No, but you can legally stick a policeman outside and prevent them from leaving, which is functionally identical.
You can also legally take them into a complex and prevent them from leaving until they test negative, as has already been done for other infactions in the US.
The executive branch in the US also has the authority to rapidly execute such measures, and has done so historically.
It is functionally identical but completely theoretical and not achievable in practice. There's no way you can achieve that level of homogeneous control in a large democracy with states that have heterogeneous beliefs and political values, which is what you have when a democracy is sufficiently large.
If New York was isolated totally and completely self governed, you have a hope of achieving what NZ achieves.
Even a country as small as Australia is evidence of this thesis. They can get it under control in one state but a cluster pops up in another and it becomes a never ending game of whack a mole. If Australia was only Sydney, covid would be a distant memory. If Australia, population of 25 million, can't eliminate it, then trying to do so in a democracy with 300 million is a pipe dream.
You've moved from saying that NZ's policies couldn't be implemented in other countries because they wouldn't be effective to saying that NZ's policies couldn't be implemented in other countries because other countries refused to implement NZ's policies. The first is meaningful, the second is tautological.
In Québec as of midnight today it will be illegal to engage in any social activity outside of work, with the sole of two people living alone visiting one another in their residence, for a period of 28 days, in the regions marked as "zone rouge"
This includes outside gathering.
The end result is that I am not allowed to engage in any in person social activity for the next 28 days, at all. The only context in which I will be able to see people outside of my dwelling will be going to work (sadly/luckily I work remote), and getting groceries.
So basically, I'm banned from socializing for the next 28 days at minimum, and so are most people in Québec.
As for your edit according to which this is only possible in large countries if they are totalitarian, the tactics China used are exactly the same that NZ has used, and are fully consititutional in the United States. Basically, telling people not to leave their homes for two weeks, using the Army to deliver food and supplies, and stopping travel between cities. These tactics have been implemented historically in the US in other epidemics and pandemics, so unless your claim is that the US is authoritarian, I don't follow.