I agree that sweeping statements about public opinion in history very seldom have any hard evidence behind them; even modern opinion polls have to be treated with caution.
Some diarists recorded what was being said in the streets which is useful but only gives a small sample.
Napoleon had his prefects reporting on public opinion in 1813-14, I don't know whether any other government had a similar system.
As far as the peasants were concerned I suspect they didn't care too much who governed them as long as they were left in peace and not taxed too heavily.