Lapistia

In my opinion, the Pain Cult has an excessively harsh penalty to health.

You can play with mana shield and negation. For pure mages, the mana shield is less useful, as they actively cast spells, while for a melee cultist, the highest bonus to health will be beneficial. And take Blightfield as their origin to further increase survivability.

Added 30 seconds later
Although, I also think they are a bit too fragile.

Added 3 hours 9 minutes later
You can also do something like this if you want to get really creative:
1) Take the ability from Dzonghyan. Choose Grimwood (get Pain Cult) and learn Tao-Ryu. Since we are interested in survivability, it makes sense to take either full parry (doesn't save against samurai and allows counterattacks) or +6 attack range (doesn't allow counterattacks, you can kite some opponents).
2) For the mana shield and negation, learn Energy.
3) We have two skill points left. There are different options for where to spend them, but I would advise taking Creation and Air for speed, willpower, and energy. If desired, you can replace Air with Assassin for more consistent critical hits and more deadly standard attacks, but the character will be weaker and slower.