b) making food from raw ingredients is cheaper than buying (at least some of the ingredients) pre-made. Again, it isn't for a surprising number of foods because, you know, economies of scale. Prime example is bread.
It is for a lot though. You can buy a kilogram of rice (or even larger amounts, price didn't move at all in Northern Germany), or you can buy the 2-minute-microwave-stuff (price did move). You can buy 2kg of potatoes for the price of 750g french fries. You can buy soup ingredients or you can buy canned soup etc etc.
Why do you think economies of scale wouldn't happen at the potato-selling business? Are they buying and selling individual potatoes?
We can go back and forth listing every single food under the sun, but the fact if the matter remains: food prices have gone up. Including for "ingredients".
It's easy to dismiss your opponent with "but rice and potatoes aren't more expensive". Well, I don't only eat rice and potatoes, and prices for other stuff like meat and milk has gone up.
a) raw ingredients didn't go up in price either. They did: https://news.ycombinator.com/item?id=35291270
b) making food from raw ingredients is cheaper than buying (at least some of the ingredients) pre-made. Again, it isn't for a surprising number of foods because, you know, economies of scale. Prime example is bread.