I think it is the other way around.

By cutting down the population of live covid virus particles in the wild, that is, living in human hosts, the possibility of a hard to kill variety to evolve will diminish by a very big probability.

In fact, the new more dangerous varieties are theorized to have evolved in single individuals, who lack a strong immune system, and can't kill a single virus infection for months, and then the virus accumulates changes over these months before jumping onto the general population.