You have to attack a randomly marked foe to fill a meter, when when it goes off gives you unlimited energy…for 3 seconds. So if the last thing you kill sets off unlimited energy the effect is gone before you find a new spawn. If you had to move because of traps, enemy effects, poison pools, big windup…again, no benefit. And the entire time you are filling the meter you are getting no benefit. The mark does nothing for you.
Combo points may require use of a basic attack but those have benefits beyond just building resources, you do not lose them for moving around, and you are always building them so they are there to be spent.
Could the mark do something else to benefit the rogue while filling the meter? Or peraps give a fixed number of attacks which cost no mana and countdown as you use Core skills?