Not just that Stu. The toxotai can use flaming arrows to demoralize enemy units. The best option would be to combine and have both slingers as well as archers in one's army. We already know slingers pierce armour and flaming arrows demoralize enemy troops.

EDIT: Scato mentioned one critical thing and that is how archers can be positioned behind your own troops as their trajectory is higher than slinger trajectory.