This is an idea that can be crap, but i want to share it.
So, we have ranged units that do melee damage, like axe thrower, gbeto, mameluke.
What about melee units, with zero range, but that cause pierce damage? This unit would do almost nothing against siege rams, but would damage better other units with low pierce armor. Being a melee unit, should they be fast? Tanky? What uses could they have?
What would be the weapon they use? A whip?