I'm not as familiar with Taiwan's measures, but the biggest difference between mainland China and New Zealand, in my view, is that China does mass testing.
When the outbreak began in Auckland last year, New Zealand was testing about 20k people a day. At that rate, it would take months just to test the population of Auckland.
In contrast, when a Chinese city has an outbreak, it will test the entire population of the affected neighborhood or city within days. That will be repeated every few days, until the public health authorities are confident that they have identified all of the clusters of infection.
What happened in New Zealand is that the public health authorities were never able to identify all of the infection clusters. They did a lot of contact tracing, but cases kept showing up that they couldn't trace back to previously identified cases. There was a low level of cryptic spread in the population that they never got a handle of. Mass testing would have addressed that problem, but New Zealand doesn't do it (and probably doesn't have the capacity in place to do it).
China has applied the rules to everyone(although you get really fancy quarantine facilities if you're important). There is also interprovince quarantine requirements.
Apparently Taiwan is playing with fire again. They have 3 weeks of quarantine(two in real isolation and 1 where you have to avoid crowds yourself), but apparently contrary to official policy some business travellers have been offered 3 day quarantine(that's how their "second" wave happened, 3 day quarantine for airline staff). The offerings were made in private meetings and not in writing though. I guess everyone learned that paper trails are bad if you want to keep outrage and accountability low.
Yeah my wife went back to China to visit family recently, and on arriving in Shanghai had a 21 day quarantine. To even be able to fly there she had two COVID tests prior to leaving UK, and one when she arrived in Finland (on way to China).
