This is misunderstanding the point. The issue is not IQ scores are not increasing less rapidly - they are now decreasing! Increases asymptotically approaching

This is misunderstanding the point. The issue is not IQ scores are not increasing less rapidly - they are now decreasing! Increases asymptotically approaching something near 0 would be completely expected. To understand why think about something like developmental malnutrition. Developmental malnutrition causes reduced IQ. As this form of malnutrition was reduced in a previously very poor area you'd see a substantial increase in average IQ. But then as future generations also have stable supplies of food, this increase would disappear as the stable food supply would no longer provide a relative increase compared to past generations. Make sense? IQs getting literally lower is something very different than IQs growing less slowly.