Wrong, what dies first is not up to the tank, it's a matter of overall Warcraft community decision on which mobs are the highest priority in every pull (and it's fairly obvious which ones are), once that is decided, it becomes the baseline strat that 99% of groups follow because it's the most efficient way to do it, especially in dungeons are on a timer with M+. It should not be up to the tank to point that out to the DPS as it wastes time, the DPS, assuming the DPS have at least run the dungeon before, should already know what mobs in a given pull are dangerous and need to die first.
I'm a DPS, saying this as a DPS, anyone who knows me would tell you I fucking hate tanking, and I still, as a DPS, am telling you it's your job to learn these things too, not the tank's job to hold your hand through the whole dungeon.