Right, that's why our ancestors didn't all evolve that mutation anyway. But our ancestral environment isn't the same as our current environment: just engineer m

Right, that's why our ancestors didn't all evolve that mutation anyway. But our ancestral environment isn't the same as our current environment: just engineer more genes to paper over each successive disadvantage, recursively, until the only remaining disadvantage is "reduced energy efficiency". Because our current environment is more than efficient at supplying humans with energy.