Everything with the armor under 10 is cannon fodder for HA, in my experience. The only "hoplite like" infantry unit really capable of resisting them is, aside from Classical Hoplites", Thorakitai - normally i only manage to kill them from uphill shooting at their backs. The large shield doesn´t really help you, since it´s the tactics of the HA to surround you, and even AI seems to know that quite well. Once the enemy HA are out of ammunition, and tired, you can send your Prodromoi to finish them off.
But in any case: if you´d be a Lord of a Bosporian Kingdom, would you try to fight a mobile and swift mounted enemy with some infantry, or would you adjust and fight fire with fire? ;)