Afaik, the big bomb doesn't best be LB'd ? 2 BRD party will have its troubles but I guess have enough dps, while in bad cases I never tried with tank's lb before detonation, dunno if oneshot anyway, guess yes but maybe someone tried, let me know.

In your cases, yes dps sitting on an aoe is always bad. Tank facing boss to group, bad too, just take note there isn't so much space to move off. Bad + bad = wipe, we all know this equation