What do you mean -1 atrition?

-1 to food thats literally the limit to food loss per turn -> attricion of reserves.

Food is essentially worthless to produce

yes food is broken so you can't take a big loss (such as -10 food/turn). it caps out at -1. you also can't make a lot of food mid to late game (caps out at +.4). also the caravan values food at 1 food = 1 turn of food. it should value food as 1 food = 1 food needed / turn.

so for example if you need 38 food / turn, right now if you buy 38 food in the caravan it will create 38 turns of food , instead of properly calculating it as 38 food to satisfy 1 turn.

Therefore, the OPs strategy is valid, but an exploit.

This seems partially fixed now with the new update that removes the caravan exploit.