They solved it as long as they can live without contact with anyone else.
As much as it shows what could be done with drastic measures, NZ is an island with small population, in the middle of nowhere so it can easily lock its borders compared to say, pretty much any European country.
They certainly handled it better, but I'm not sure that they will actually be ready to live in a COVID world any time toon without a strong and thorough vaccination rollout like everybody else.
Wanting to keep zero case as all cost is going to be increasingly difficult and expensive to maintain: how long will the population accept that they can't travel? Can an economy partially dependent on tourism afford not to be open? Wouldn't NZ be penalized at some point if business people/athletes/students/engineers/scientists can't fly to or from it?
Even if all western countries had been exemplary -ignoring that it would probably be impossible anyway- as long as we don't ensure that even poorer countries are able to stamp out the virus, there will always remain sources of variants that will continue to spread across the world.
Look at Australia. Small population, big country, huge barriers to entrance (even for residents), extreme quarantine measures, and yet, you only need a single infected person to start spreading again.[1]
As long as the population won't reach the minimum vaccination level required, they will continue to be barred from travelling and get lockdowns.
Looks like the only hope we have is to accept it's there and ensure that the impact remains manageable through vaccination and targetted health control measures.
[1]:https://www.nytimes.com/2021/06/26/world/sydney-lockdown-cov...