Even so, slingers should not be able to shred armoured hoplite units from 20 meters distance, not giving them time to close in before they melt.

Further proof that the whole ranged mechanic is broken: Eprius starts with merc. Africa elephants, right? I focused them with 6 units of slingers. They stood there, 2 elephants dying for the duration of several volleys. And suddenly, after some threshold of hitpoins or what have you was reached, the remaining 10 dropped as if they were headshotted by SEAL team 6 simultaneously.