Refusing the give fight to a chariot oriented army versus a non-chariot based army would seem to also be a big factor.

If you don't have chariots and they do, just fight where the chariots can't.

You probably look very kingly fighting from a chariot. Raised up platform, but also standing.

You get an archer with extra mobility AND the ability to focus on hitting his target while someone else does the steering AND armor AND a bigger carrying capacity (more quivers of arrows, ...)

yes, I know the stories of the amazing accuracy of horseback archers (mongol, native american, ...). Just saying that the 2-man thing may be more efficient than you give it credit for.

Personally, I think I would rather face N Persian chariots, than 2N Mongols on horseback. I wonder if anyone has done a comparative test?

I think they are separated by around 1500 years, so I’m sure the Mongolian army would be scarier. But the Alexander-era Persians wouldn’t have that choice, right? For example stirrups and advances in composite bows (they’ve existed for a long time, but were high tech things, so I’m sure every culture iterated on the idea and 1500 years of iterations add up) probably made Mongolian horse archers a lot better than the options they had.