It is true that the lower the rate of infection, the lower the "breeding ground" for new variants to develop. Unfortunately we are living in an age where numbers are everything, and people have lost track (to some degree) of reality. For example, big pharma employs hordes of statisticians to process their data and establish "statistically significant" differences that they can use to justify a product as being effective. Science has adopted this approach, but does it have any real world significance, or is it just numbers?
For example, this weekend I was reading about a U.K. report in to the effectiveness of the AZ vaccine at preventing the transmission of the delta variant. It considered the transmission of delta in "break-through" cases, i.e. people who contacted delta despite being double vaccinated. The data was that AZ was "very good" at preventing transmission of delta in break-through cases occurring soon (two weeks) after the second dose of vaccine. However that effectiveness dropped to almost negligible by three months after the second dose. So, "very good" transmission prevention - that means that the chance of passing delta to a close contact is fairly low, right? Wrong. The chance of passing delta to a close contact under those conditions is 57%, which I don't consider "very good" protection. If you were told there was a 57% chance of getting a disease, would you consider that to be safe? So what about "almost negligible", what is that in actual numbers? Well it turns out that "almost negligible" means that there is a 67% chance of passing delta to a close contact, which is about the same a with no vaccine at all.......
So the "very good" reduction in transmission of delta, two weeks after the second vaccination, actually means a reduction from 67% to 57% in the chance of passing it on. "Statistically" that's significant, but in real world terms? In either case it means a close contact is more likely to catch it than not!
The numbers for Pfizer, by the way, are 48% after two weeks and 58% after 3 months, so marginally better but still not "protection" that I'd be risking my life on!
Obviously this is looking only at transmission, and the other benefits of reducing the seriousness of the symptoms still remain....