My layman understanding is that it doesn‘t work that way.
Less spread = less chance of mutation = less chance of uber infectious new flu strain.
We go for a suppression strategy instead.If 1 person infects 1 other person (as we seem to be trying to achieve with corna) it is going to take 1000 generations before full immunity is achieved. There is going to be far more chance of mutations in 1000 generations of viral replication than in 3 generations.
However, I think this is right in one sense: an implicit or explicit strategy of keeping R0 as close as possible to 1 would be the strategy with the highest risk of significant mutations, as we have seen.
UK government ministers literally stated this to be their strategy.
Comparing places that didn't lock down to those that did I think its fair to say that the strategy has not been effective.