Oh, I may have stated things poorly — no, I am not talking about the rate of mutations, per individual or per unit of time. Yes, those can increase under stress. However, each of those mutations is like a lottery ticket — it has a certain probability of ‘winning’, being a trait that increases fitness. For the sake of example, suppose the chance of winning was one in a million billion — in terms of combinatorics of amino acids forming useful proteins, that’s extraordinarily generous. Then, with a little bit of logarithm rearrangement, we see that we have a 50/50 chance of a winning ticket after about 700 thousand billion tickets. That’ll be true regardless of the temporal or individual rate of mutation. Is the difference with what you pointed out clear, there?
Then, if we observe organisms which uncover winning tickets at a frequency among tickets of only one trillion tries, we would have to find an explanation for how organisms were uncovering winning mutations after so few attempts. That is where quantum operations, to search that space of mutations in parallel, might be handy. I hope that made sense!