Now we played our duel on a small map: No ancient ruins, start in classic era. No CityStates there (I don't know why). Many Barbarians everywhere. Plenty resources, but only 4x2 horses on the whole map.
The Huns started almost in a corner and I founded on a 2 horse spot. Research on Mathematics to build horse archers asap. Meanwhile we built Ekis.
Exploration did not take long and we found Mongolia's capital, and another horse resource close to the map's center.
We founded our second city almost at the same time.
Then everything developed very differently. We built 4 horse archers.
The Mongols built one or two horsemen but no skirmisher.
Not a single one in the entire game!
We declared war and succesfully attacked and took their second city.
They asked for peace and we accepted.
Next turn they stole the horses with an ordo.
Some turns later we could place a counter citadel and regained the 2 horses, built 2 more horse archers and declared war asap.
Mongolia lost their capital and offered capitulation some turns later.
Result: I could not recognize any change by AI unit prod mod. Maybe because it is the UU of the Mongols?