Particularly with a generational time of 15-25 years, and with the fact that evolution basically stopped working as an enhancer once humans passed the threshold of preventing most premature deaths (where premature just means before the end of the reproductive window).

This is way off for almost all of human history almost everywhere. See the work of Greg Clark: occupational success and wealth in pre-industrial Britain were strongly correlated with the number of surviving children, as measured by public records of birth, death, and estates. Here's an essay by Ron Unz discussing similar patterns in China. Or look at page 12 of Greg Cochran and company's paper on the evolutionary history of Ashkenazi intelligence. Over the last 10,000 years evolutionary selective sweeps have actually greatly accelerated in the course of adapting to agricultural and civilized life.

How did intelligence, or earnings affected by intelligence, get converted into more surviving children?

• Average wages until the last couple centuries were only a little above subsistence, meaning that the average household income was just slightly more than enough to raise a new generation to replace the previous one
• Workers with below-average earnings could only feed themselves, not a pregnant wife or children
• Men with higher earnings were thus more likely to marry, and to be able to afford to do so earlier, as well as paying for mistresses and prostitutes
• Workers with high earnings could give offspring more nutritious diets, providing increased resistance to death by infectious disease (very common, and worsened by nutrient deficiency or inadequate calories)
• High earnings could be used to build fat reserves to withstand famine, and to produce or purchase enough food to sustain a family through those lean times
• Intelligence is helpful in avoiding lethal accidents
• Likewise for execution for criminal activities, falling prey to crime, and avoiding death in war