I think that healing is only better than herbalism early on and only when it's past 70-80 or even maxed.
At a later point, you just find enough PV and healing herbs to offset slower regeneration.
Past 20 PV you really don't need natural regeneration/healing that much and for emergencies you have potions and prayers (which you should have aplenty by this point).
Farming herbs without herbalism is painful and very ineffective, no matter how you look at it.
Blessed spense is so much better than uncursed, plus you get plenty of other useful herbs and in a fraction of time it takes to farm similar amounts without herbalism.
Preferably if you can get gardening too, you will maximize gains from herbalism with quickly farmed hundreds of blessed spense and little time lost.
If I have a choice, I will always go with herbalism+gardening versus healing, even if I'm not candle.
For herbalism alone, you're left to take the little scraps that RNG throws at you - one patch here, one there, 3-4 in the big room once you clear the rat infestations, worms, spider factories etc. so it's a bit harder.
If I were a candle troll assassin, I'd definitely go for herbalism and then wish for gardening at some point, sooner rather than later.
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