With the amazing quality of garrison troops, no probably not but more of your stuff would die since it's more confusing =p

If -you- are defending, it is entirely possible for settlements that spawn just one sort of good melee unit for its garrison army to win a battle against all odds simply by only having to fight the AI on one road, because it never uses any other roads or any flanking, so you can keep your crap units away from the main fight, ensure they don't rout, while at the same time creating a killing zone, where especially low quality AI armies like to mass rout in a 3 minute battle from what started as a fight where the odds were 3:1 in their favour.