I think logic can easily explain why units were used in a harrassment role, they didn't have very much ammo.

When archers did have ammo, they were incredibly effective, at the battle of Carrhae, Persian archers firing from horseback with a basically infinite supply of arrows from a nearby baggage train put down 20,000 Romans, mostly with arrows... To be fair many were killed in the frantic retreat, but obviously arrows were effective enough to get them to route Roman Legionnaries, despite them being in a testudo. The fact is they were being killed at a fast rate.

I would think archers wouldn't be so effective because they didn't bring so many arrows to the battle, not because their arrows were ineffective. I don't think that even the most prepared archer brought anymore than 20 arrows... probably around 10-12 for most. And if 3/4 miss, that is only 4 arrows on target. So 2 archers put 8 arrows down on target, and I'd like to think one would kill.

I don't think single units took 2400 arrows either back then... but you can do it in RTW...

Anyway, this is obviously unforunately a matter of opinion, whether you choose to believe logic, or ancient texts (just be careful with some of them like the Bible!), is up to you.

Either way, if EB is ported to 1.5, how are you planning to deal with the archer bug? I should hope you'll develop it so archers shoot at heavily armored unit...