Are you suggesting that isolation measures / social distancing won't help flatten the curve, because this is not an influenza virus? If so, walk me through your reasoning.
Mutation is largely a numbers game - the more replications, the more opportunities for mutation. The more mutations, the more opportunities for an "unfortunate mutation".
Social distancing spreads the viral replication over a longer period, it doesn't increase the number of replications.
If anything, it decreases the number of replications, since measures that flatten the curve also tend to reduce the area under the curve (i.e. total number infected). And it may also allow for less replications per individual, if anti-viral therapies have any success.
Finally, flattening the curve allows for more time to develop antivirals and vaccines, which also reduce the number of replications.