Archers are pretty useless for the most part - they do nothing to phalanxes or any unit with a decent shield.
The only way you will get any kills is if the AI is dumb enough to let their cavalry sit around doing nothing, or they turn their backs on you.
Slingers are far more useful due to the AP bonus against armor.
My levy slingers get more kills than my damn "elite" Cretan archers most of the time.
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