I've had thoughts on similar lines to the top level comment, by the following line of reasoning: In US and Europe, policies and behavior (such as mask-wearing

I've had thoughts on similar lines to the top level comment, by the following line of reasoning: In US and Europe, policies and behavior (such as mask-wearing and social distancing) have become stricter as the number of cases rise and more lenient as the number of cases fall. This means that the reproduction number hovers around 1. If we imagine that R_0 for Covid-19 is 2.0, no measures are taken, and a variant which is twice as infectious appears when there are 10^6 cases (in a population of 10^9), then the variant will have only infected ~10^6 people by the time we have herd immunity (a very rough estimate). On the other hand, if measures halving the spread rate are imposed when 10^6 cases are reached and the variant appears, then the variant will still spread exponentially while the original strain is curtailed, resulting in most people catching the highly infectious variant. I have no background in medicine or epidemiology, so I'm keen for people to point out flaws. Edit: I am not advocating that no measures to stop or slow the spread of Covid should have been taken.