Actually I think there needs to be a balance?
If the tank is bad, no one can live.
If the healer is bad, no one can live.
If the DPS are bad, the fight can take a hell of a lot longer and it's most likely that no one will end up alive.
DPS can be handled with. Personally I've done a ZA with a kitty-druid who was pulling 6-7k. Not one wipe. Not one complaint.