Pikes on wall are problem. They do not use secondary weapon and they form formation anywhere even if it means that 6 are on bottom and 250 are on top of wall. This 6 man on bottom can kill whole elite unit while rest is stabbing the air. If other units get stuck with them they got bonus (in fort - or something). So peasants can kill whole elite unit.
This is old problem and it is recreated again. I remember that removing secondary weapon from pikes in medieval created same result. Pikes become unbeatable and unbalanced (they have fast animation). So i had very strange expirience when my 1000 Triari get massacred not by whole pike unit but from 6 men. My Hastati routed by unarmed rabble. 100 men in few seconds. Faster than elephants.