I think you're right that focusing on group effects will be more productive, but I probably reach the same conclusion for different reasons :)

I intuitively don't like the idea of the 10x programmer, my core argument is actually that you should not try to become a 10x programmer, and that there's no order of magnitude productivity you can gain in a vacuum, ignoring group dynamics. So you shouldn't focus on individual performance too much! There's not much you can do about it, anyways

Managing groups of people is hard, and there's often big inefficiencies that are going to be obvious to some people (engineers love to complain about management!) but that have a true multiplier effect when fixed. Because for the time invested, you have an effect on the whole team. That's a true multiplier.

I don't know what specifically you think I should learn about the fallacy of reification, but please feel free to elaborate.