Archers/Alexander

Overall strategy
Unlike the vanilla unit in Rise of Nations, Archers in Alexander have an altogether different unit designation -- they form light ranged support, and are not used for attacking heavy infantry -- at least not the heaviest units like Thebaiot Hieroi Lochoi or Persian Javidan, but are instead meant to counter the units that are traditionally used to counter such units -- namely, Skirmisher Levies, as well as more powerful units such as Hellene Akontistai or Persian Takabara.

Archers, unlike Skirmisher Levy units (and their cognates) are meant to counter unarmoured units, and function best against enemy light infantry. It is true that some more powerful archer units such as the archer version of Javidan, or the horse archers of the Skythoi and the Sarmatoi are capable of armour piercing attacks, but overall, low-level archers, such as those fielded by the Aigyptoi or the Boii (or even the Hellene Toxotai) are still better used for damaging any enemy unit that isn't well-armoured. For heavy ranged support, you are advised to use Composite Bowmen instead, if they are on hand.