There’s some issues with your assessment.
You are correct that the cost is the same; however, you still have to fill the exp bar and the rate varies wildly. If I use 1* off color fodder, that will take more fodder (as you state, it is per individual fodder card) and therefore more food than even 1* on color… let alone 2* off/on color or higher tier cards.
As a result, it’s nowhere close to the same amount, it depends on what fodder you are using explicitly.
Also I’d note using 10 fodder heroes at a time is not necessarily optimal; really if you’re trying to be hardcore about it (I’m way too lazy and the savings is absurdly trivial) you want to come as close as possible to maxing out your current level, regardless of the number of feeds that takes, and then do a big 10 feed to minimize the food used.
Maybe we’re getting at two different things, exp is a full measurement, but you used an individual measurement for food costs… without looking I was assuming you were doing both full measurement, and you can’t really do that on the food side.