Great example in Portugal - election results predicted by the pace of the Reconquista: https://threadreaderapp.com/thread/1181292177130999808.html

Your counterargument proves too much; if "people" don't have agency then you can't blame anyone for anything, including being unable to blame the Mongols for anything about modern China. The concept of blame becomes entirely pointless.

This may, in fact, be true. But in this specific context, it's an argument that proves too much.

Psychohistory is pure fiction. The closest real equivalent is economics and economic predictions are essentially always wrong. I don't remember where exactly, but I recall reading that someone had done a mass study on economic forecasts and discovered that the only time they're correct was when they were predicting a continuation of whatever the current trend line was. Forecasting never managed to predict an actual change to the status quo, making such forecasts useless.

We can't even measure GDP accurately in quarters already passed, let alone predict what it will be in future, and surely predicting the movement of GDP is the most basic task a psychohistorian could possibly set themselves.