The original blog goes into a lot more detail, including the mechanics, logistics and risks of foraging.

The solution to getting around the wagon equation is ships, ships could carry tremendous amounts of food, with a minimal crew and thus minimum consumption, only problem is ships are expensive.

On donkeys, typically armies used mules and draft horses instead of donkeys, because of behavioral and maximum load reasons, and grazing is not enough for mules and large horses, also on certain seasons there is not enough grass for animals to graze in the terrain either.

The original blog has also a piece on nomad logistics, who used significantly smaller horses that can be sustained only by grazing, these armies were able to traverse a lot larger distances, hence the success of the mongol armies.