You stop having issues on drk in dungeons when you figure out how to weave your mitigations properly and get paired with a healer that knows when to cover the gaps in your defense. Once you hit that, you'll never drop below 60% health.
The issue is that if you get into a bad situation, you have no way of getting yourself out of it, and roulette healers are all too eager to turn their brains off and allow that bad situation to occur. That's why my runs with SCH have always been smooth.

GNB has the same issue, but if it all goes to shit, you at least have an invuln to fall back on. Drk does not have an invuln.