My suggestion would be serious tanks. Like, really serious.
They would have so heavy armor, that they can only walk, not run, but it would also give like 70 body and head armor, with slow, relatively weak weapons and powerful board shields, making them ideal for shield walls and holding off attackers.
Example:
Weapon proficency: 50 in everything, except croossbows with over 100, to give them something to do until the enemy reaches them.
High strengh ~40 and high iron skin ~8 with 0 athletics and about 10 agility
If they were any stronger than that, they would just bash into their enemies, while igoring the little damage they take.
Equally, there should be "Hunters" in more factions, classes which are really fast but fragile. Of course, they should be absolutely crap with ranged weapons, with too little strength to use firearms or heavy weapons.
Example:
Weapon proficency: ~120 on all melee, 20 on ranged
Strength ~6 Agility ~50 and athletics 10, iron skin 0