Dear melee DPS...

[Zfz]

if a tank/healer can't handle that extra pressure, the tank shouldn't be multipulling

Tanks use cooldowns to manage AoE packs. There are no tanks in this game capable of maintaining the same damage reduction indefinitely. A pack of 8 may be perfectly survivable while 40% damage reduction is up; but it will become a heavy drain on healer MP when it runs out and you go into 20% damage reduction, and it may finally be fatal (i.e. only lucky crits from the healers will have any chance of keeping you up) when you run out of defensive cooldowns.

It helps tremendously to reduce a pack of 8 down to 6 or 5 by the time the tank's major cooldown has finished. With less incoming damage, the tank will be able to maintain the same healing requirement when he only has access to less powerful cooldowns.

8 enemies * 500 dmg per 3 seconds = 4000 per 3 seconds, @ 40% DR you take 2400 per 3 seconds
6 enemies * 500 dmg per 3 seconds = 3000 per 3 seconds, @ 20% DR you take 2400 per 3 seconds

v.s.

8 enemies * 500 dmg per 3 seconds = 4000 per 3 seconds, @ 40% DR you take 2400 per 3 seconds
8 enemies * 500 dmg per 3 seconds = 4000 per 3 seconds, @ 20% DR you take 3200 per 3 seconds

Now add to the fray some mobs that may surprise the healer with a party-wide AoE hitting everyone for 2k. Or a PBAOE with petrify effect for 6~9 seconds. Or a stun on the tank that happens to coincide with a telegraphed AOE hitting the tank for 4k, followed up by auto-attacks that will land 100% because the tank is stunned. All these are easily avoidable if the tank is given time to act. But stun resist builds up and mob casts may overlap and sooner or later one of these casts will come through even if you have the world's best tank player at the helm. These are the types of enemies that should be killed asap.

These numbers are all for illustration purposes and aren't actual in-game numbers. But the situations described are all real.

If the party has enough firepower to always finish packs within the tank's cooldown, then sure, why not. Do whatever you like to maximize your total dps. But otherwise it can be a big disservice to both the tank and the healer to try spreading out your targeting so that you're always maximizing your AOE dps.