The bigger picture is obscured from your on purpose. The best game strategy is to work with the "world you know" and not what you want it to be. My OTL example was an attempt to explain to LM why there are no horses in the Animas and give an example from RL how such a thing can happen.
I can assure you that Inowe is not just a simple transposed RL arrangement. There is a plan and it will unfold. The world is such that those of you who long to lead raging hordes of barbarians can do so, but you might, for the time being, have to think differently about how that could be done without horses. Offense, defense, fortifications, tactics all change when horses become elephants. If such things are beyond you, then stick with infantry.