Why mark targets?

[baopee]

Because those aren't readable without manually clicking off to every target, which interferes with the ability to deliver skills on GCD to your primary target.

Also, your second graphic is actually showing the health bars of the enemies remaining on the field - not the threat. In the pic:

Top Shade Seeker is T; full health, full bar
Middle Shade Seeker is R; partial health gone, partial bar, to scale.
Bottom Shade SEeker is Q; full health, full bar
Clam is S; partial health, partial bar, to scale.

People like marks because many tanks don't Flash regularly enough to keep AOE threat established. No good DPS wants to overrun the tank.

what i meant to show on the second picture was the enmity indicator, the bubbles before the HP bar of the mobs.

[Bridgeburner]

what i meant to show on the second picture was the enmity indicator, the bubbles before the HP bar of the mobs.

You can see the limits to the utility in this picture, too, though.

A solid red orb means you have threat, but by the time that orb changes to a red triangle, you're typically already losing the monster's focus.

Additionally, as demonstrated in this picture, you only get those floating health/threat indicators on enemies you've attacked. This picture shows the Princess and two Soldiers, but the threat/health indicators are only showing two of the three targets. (The person taking the photo has not interacted with/done damage to/established threat on the 3rd target, thus no indicator.)

... out of curiosity, why's the DPS fighting Soldiers in Cutter's Cry? Usually Heals secure aggro and sprint 'round the outside to let everybody focus the Princess down, no?