the ideal solution would be if pretty much all macedonian (and helleinstic) standing army infantry units, were capable of fightng with 3 sets of weapons; sarissa+the macedonian shield, javelines+swords+pelta shields, and traditional holite way of aspis+doru+variaty of short swords. thus the infantry could be used in different maners for different purposes (holding a line in field battles in opposition to assults on fortified possitions or flanking actions). however the RTW engine does not support this many weapon/shield combinations so i think the team went and developed these variations in different unit types. to be honest i don't see a better alternative with the current engine availabe. even in MTW2 things are the same.
Exactly. I think that the hypaspists can fight with several weapons, depending of the situation (siege, battlefield, ambusher). A solution it's maybe 3 units of hypaspists, the phalanx type, the hoplitai type used by Alexandre and the peltast type used by the late successors. But it is clear that it is not good to encumber the unit slots available.