Drain was such a bad tool that you neglected your fundamental job function by using it. Doubly true for BLM since they had very little to offer in the way of party utility, making DPS the only reason for including them.
As others have pointed out, the heal was awful to the point that you'd have to sit there and spam it in order to recover significant HP. If you're spamming Drain, you're not doing meaningful damage and have no reason to be there. Better to take the death and get a party with healers who are awake, because it would save more time.