Farming subsidies are the only way to prevent famine, the granary system sort of works, but regularly resulted in shortages and famines throughout every empire in history. Even not accounting for longer term climate trends, yield due to weather can vary up to 30% in a year, so it only makes sense to pay for a bit of over production so in the event of a couple bad years your food output is merely break even, and not 70% of needs.

Its better to pay 5 cents more for a loaf now than pay $20 a loaf with rationing later, or if we went back to granary system possibly getting moldy food.

Isn't the point of rationing to prevent the loaf going to $20.