Yeah, if nobody is stunning eruptions you pretty much have to worry about yourself and the tank. Heal the other people if you have time, but let them die if they're crossing eruptions over each other and you can't cover all the damage. After nails, there's no DPS race so it's just survival at that point. Don't stress it too much. Also, the tank sounded like a jerk. It's okay to not stun eruptions, but he shouldn't blame less experienced players for dying if he makes that decision.
Basically, just do what you can and get used to dodging eruptions because some are probably going to get through, even if someone is stunning. As previously mentioned too, a DPS stunning on cooldown can lead to the same situation without it even being the tank's fault, so it's just something we have to prepare for.