The foot man has two upgrades the archers who dishes a lot of damage and the Knight who can take a lot of damage.
I believe the herbalist should have two upgrade paths as well the cleric who heals and buffs allies and a shaman or something different to curse and damage enemies.
They could act opposite to what the cleric does casting spells on enemies to make then slower, turn on there own,and lower attributes like muscle or courage. instead of healing they may cast spells that steal health from enemies. They could also have a aura that makes the enemy more likely to flee and lowers attributes.They could be a shaman or a Sorcerer
since they would wield dark magic that hurts not heals.