I would say the level 5 is the only one that needs re-balancing.
A 6-16 I would be better all around with the spirit of the Occultist without it being trash 0 heals from time to time.

Torn between using this one and the one that has lvl 5 at 5-15 (better numbers, but that one removes the bleed, unfortunately).

I'd suggest changing it so the minimum heal is (bleed dmg per turn) + 1 instead, so the minimum heals are 2, 2, 3, 3, and 4. That'd relieve the main problem with Occultist (0 heal + bleed) that leads to RNG deaths and allow him to perform in comps without having other characters with heals to prevent deathblow if rng screws you over, while maintaining the occultist's appeal of big heals. Otherwise, at rank 5, his heal is basically the same as vestal's (9), meaning you have no reason to use the occultist as a healer.

What I do with occultist is spam cleansing stone/similar trinkets to make his bleed chance stupid lo. The tradeoff that some people won't like is that he won't be much for debuffing after equipping the trinkets, but I play him for the chance at great heals. His risk/reward healing has come through for me more often than not.

He's bad compared to Vestal. Bad luck literally gets your characters killed. Consistency matters..

The vanilla occultist isnt a bad healer. Revise your team comps if you are having trouble with him, I have 4-5 occultists on my roster every playthrough and they perform just fine.

Hmm, sounds Similar to the "Occultist Heal Improved" mod, but with a slightly higher Minimal roll. While I do like being able to count on a heal, I rather like having a feeling of a gamble with the Occultist. I'll try it out to see if I like it.