So in my mind the problems with proposed Mounted Archer ideas are namely that the unit would be
A: Too powerful and too spam-able (hence the rework of the O.G. Tridention).
B: It would displace the need for both Riders and Archers
To solve this I have come up with what I believe is a balanced Mounted Archer
Cost: 4/5 Stars
Attack: 2
Defense: 1
Range: 2
Movement: 2
Health: 10
Skills: Escape
I would like to emphasize the LACK of the dash skill.
This way it would not compete with the niches of the Archer or Rider. We could even make this unit 3 stars by dropping the defense to 0, which would be fitting given the -1 for the mount and -1 for the bow.