[Dedas]

Rangers work quite well because most players don't have the sense to deploy counter archers. Remember that rangers don't have any shields, no helmets and only protection 8 leather armours. As they only shoot every other turn they get eaten by the standard tactic: one group of armoured missile units front, another group of cheap standard archers back. Trust me, I've been there. Facing shielded infantry is another thing they are bad at.
No I rather use them in small hidden groups following your army instead (ranger captain + 10 rangers). That way your enemy won't anticipate them and they can slaughter freely. The ranger captain with his high precision could also be fitted with a cool missile weapon to make him a mini ranged thugs. 4 or 5 of them with accompanying rangers. Perfect for that extra unexpected umpfh to your army.