I'd like to start giving people the option of commenting on shorter Cold Takes pieces (which I don't cross-post here or provide audio for). I'm going to use this post for that: I will generally leave a comment for each piece, and people can leave their comments as replies to that.
The estimate for the increase in effective population should take into account that for extraordinarily talented individuals, the chances to become acclaimed scientists or artists probably increased less than for the average person. For example, someone like Beethoven was probably likely to get musical education and the option to pursue his talents even around 1800. This suggests that the size of the effective population should increase less than linearly in the number of people with access to education.
Similar stories can be told for other factors that drive the effective population growth. (I could not figure out if these considerations are reflected in the estimates.)