Omicron is not "so mild". It appeared to be mild in many other countries due to high vaccination rates and/or prior infections/deaths. This is not the case in China, where prior infections are very rare. And although the headline stats for the initial 2-dose vaccination rates are good, they didn't use the more effective mRNA vaccines, probably don't have a high recent booster rate, and most crucially, the vaccination rates among the elderly is relatively low.
Look at Hong Kong for a sobering example. They've never had any large outbreak during the entire pandemic until two months ago. Now they're averaging almost 200 Covid deaths per day, on a population of 7 million. Per capita this is worse than the peak of the Alpha and Delta waves in the US or UK. If a big outbreak like Hong Kong happens in China, they might be facing 50k+ deaths per day.
Hong Kong and mainland are totally different. Vaccination rate is very high here and you have been able to get booster shots for months. I agree with your second paragraph though.
Look at Hong Kong for a sobering example. They've never had any large outbreak during the entire pandemic until two months ago. Now they're averaging almost 200 Covid deaths per day, on a population of 7 million. Per capita this is worse than the peak of the Alpha and Delta waves in the US or UK. If a big outbreak like Hong Kong happens in China, they might be facing 50k+ deaths per day.