Yes, people smoke cigarettes, and let's assume for the sake of argument that it counts as "significantly harmful". Now imagine (hypothetically) that the same mechanism of thought also causes them to pursue lifestyles that grant them an overall 20% increase in healthy lifespan as compared to nonsmokers. In that scenario, the bias that causes smoking cigarettes is not "significantly harmful on average".

Now consider another hypothetical where people smoke cigarettes due to their biases, and other people without those biases have a significantly higher incidence of being run over by buses. Then, the biases that cause smoking cigarettes are not "significantly harmful on average" as compared to the alternative.

I can imagine a universe where Omega goes around and gives a hundred dollars to each person who is susceptible to some bias. This doesn't mean that this example has any connection to the real world in arguing that the bias is somehow a good thing.