Why wouldn't Druids have knowledge of creating a true spell from nature?
Well its just my opinion but herbalism at the moment is rather unbalanced craft. It gives too good benefits. The way i see herbalism is that you should be able to make very basic healing potions only, maybe lesser restorations and some cure diseases. All those nagative protections, true seeings, see invises.. all those are way too potent for that craft.
And since absolutely everyone uses all those spells through herbalism, its easy for native to say "chillax man, its natural to see invisible people becouse its given by nature!"
Its just plain wrong imo, Now thanks to herbalism every character has a invisible multiclass on them, cleric. Although its low lv version its still there.
What i would rather like to see from herbalism is that it would give some unique effects, something we cant get from spells, something creative and new. Alchemy is basicly a step in the good direction, we get better and unique varnishes on the weapons and neat granades. Dont know if theres anything else on alchemy