Time to bring up another relevant thread, I guess. A ton of ideas had been shared over there, including some recurring ones, such as illnesses.
My personal favorite from that thread was the one where “negative buffs” would stay for very long with the hearthlings, and only herbalists could remove them. As well as the suggestion to make potions be carried by fighters into battle for emergency use.
The primary problem, as had been pointed out many times in the past, is that clerics and herbalists share the exact same purpose, but clerics do it 1000 times better.
I do agree with the suggestion of splitting their paths. Then, clerics would remain the field-medics, while herbalists would be more of a “mad alchemist person” sort of thing, making weird stuff from random plants.