That's why you should stick to han job.
If this is 2020, I agree with you, the more case with free transfer would have mean more chance to mutate.
Problem is, WE AREN'T IN 2020 anymore, we are closer to 2023, and people are largely vaccinated in the west. Which mean even if they do get it, the virus will not present a problem to their population because 95% of the west (97% in Australia) already have autoimmune response to that virus.
That's not the same in China, with less than 85% of population being vaccinated, you are talking about a more dynamic non-interfered transfer. Which mean it is going to be more serious in China, because based on the probability, the virus went unchecked would be higher in China due to the low vaccinated population, thus creating a bigger reservoir to harbor the virus.
Again, you said you are good at maths. Now tell me, which one would have worse in the case of community infection? A country that has 98 out of 100 people vaccinated but move freely or a country that have less than 85 out of 100 people vaccinated but limited their movement??? Dude, just because you can't move that does not mean the virus can't either.
Mind you, 98 out of 100 in Australia means only around 500,000 of the 24 million Australian aren't vaccinated. 85% in China means 195 million Chinese weren't vaccinated.
Dude, you know you were losing when you started to switch argument.