I think a decurse potion would be an awesome addition to the game - there are only three classes that can remove DoTs, and especially with harder content, those poisons can melt your face off in no time.
The restrictions from being a potion would imo be enough to balance it:
- You have to prepare and equip them in advance.
- It takes a while to drink them.
- You can only use one hand while you drink it. No class can fully function with only a single hand, and many have to pause combat entirely.
These restrictions force the player to momentarily pause whatever they are doing, and also mean that you can’t use them as an instant decurse to save yourself from, for example, Crystal Flame. This would prevent the potions from making the healer’s or mage’s Decurse redundant.