Well, regarding Rhodoks with awlpikes, I gave all shorter spears an overhand attack with a shield in addition to the normal thrusting attack. Still, it suffers from the same polearm problem (i.e. being too close nulls attacks) and the damage is rather minimal. So, they aren't too great but they can still do what pikemen in the middle ages were meant to do, and that's hold off horses. Although that requires a human player commanding them mostly. For AI they are only really a threat with their throwing spears, which is why I gave them such so they weren't stuck with pikes only.
As for mercs performing a unique role, mine are basically for taking captives as they all have blunt weapons. For instance, the merc crossbowmen have, instead of sword and shield backup like other xbowmen, a sledgehammer, the merc infantry carries a mace, the light lancers also carry a mace for backup, etc. Mercs rounding up captives to ransom or sell into slavery made more sense to me I guess and if you're playing a merc/brigand/freelance/etc. and want to use merc armies you probably need the money from selling/ransoming prisoners more.