China's policy reduced the death rate by a factor of about 75% relative to the US.

The zero-Covid policy kept Covid out of the country until an effective vaccine was developed and deployed to about 90% of the population. The main problem was that there's a widespread belief in East Asia (including in Taiwan, Singapore, etc.) that vaccination is dangerous for old people, so the vaccination rate was lowest among the most vulnerable group. A lot of old people simply refused to get vaccinated, despite large vaccination drives and public messaging asking them to do so.

Then, as you said, the zero-Covid policy was eliminated overnight, and practically everyone in the country got Covid within 1-2 months. However, because most people were vaccinated, the death rate was far lower than in the West.

All in all, the zero-Covid policy saved several million lives in China. This is based on retrospective studies by outside researchers, not on official statistics.