[pm90]

That seems to be an incorrect understanding. Selective pressure is only one of the factors influencing how frequently the virus has mutations. Self correction mechanics in the RNAs replication seem to have a much more stronger effect, since they “correct” the mutations. The article specifically mentions that the timeline for significant mutations is likely in the order of a few years.

[pharke]

A slow mutation rate reduces the rate of change if all other variables are equal but increasing the selection pressure can drive that rate of change higher by clearing the field of competitors and providing only one clear path to success.