On a fortress of the city: “Many Spaniards who have seen it, and who went to Lombardy and other foreign kingdoms,” he adds, “say they have not seen another building like this fortress nor a stronger castle.”
In any event, the advantages of stronger pack animals are only significant if you can create wheeled carts. The Incans, like most Mesoamerican civilizations, had limited access to metals and advanced metallurgy preventing them from widespread usage of wheels as a means of facilitating travel. Without wheels, the amount of distance most animals can go while carrying their supplies is fairly similar.
If I recall correctly, it is something on the order of 150 km, regardless of horse, ox, or even human. If you have to carry your food and water you can only go around 150 km with what you can carry. That means proportional consumption rate is highly similar, so two animals that can carry 100 kg is not materially different than one animal that can carry 200 kg. Under that model you would probably actually prefer smaller pack animals to reduce concentrated risk of animal loss and improve maneuverability.
You actually can do better since animals like horses can efficiently graze, but that heavily limits your transportation speed and weight maximums for commerce purposes and you still need to feed the humans.
Incidentally this is why rivers are so important in early civilization. Barges on rivers bypass the fundamental distance limit even without wind. Floaty boat and a stick to push off the banks/riverbed dominates almost everything else for commerce.
[1] https://www.cambridge.org/core/journals/renaissance-quarterl...