Mounted Archer is a short range class in Early Middle Age. Unlike other short range, mounted archer has the speed as fast as cavalry class, but low attack, low defense and shorter attack range. Having attack bonus on rocks. Effective against heavy class.
Although it looked like cavalry, it does not benefit from cavalry class's bonus and can get on rocks and swamps. Thus, it is still vulnerable to cavalry due to the combat bonus of cavalry against short range.
The tactic of using mounted archer is quite different from other units as it combines the advantage of both range class and cavalry class. Combine mounted archer with other cavalry is an idea way. As both can charge to enemies to give out attack.
Surprisingly, Mounted Archers are also effective against artillery class as they are possible to start attack in the 1st turn, even more deadly compare to melee cavalry.
A combination of 8 mounted archers is also an effective defense strategy.