Offense is kill speed.
Defense is survival time.
An immortal that one shot kills everything is what happens when offense and defense have no opportunity cost. Such a situation can not occur in balanced PVP.
Therefore , we need opportunity cost. With the current attribute system there is few cost. Most items will have at least 2 attributes.That means most items can have defense and offense at the same time. The problem here is items with even more attributes. Players are getting all the attributes they want with additional attribute slots to spare.
Another problem is with available attribute selection, defense in particular . There are very few meta options for defense . There is basically only health. Armor is not available on half the items, which effectively makes it impossible to substitute for damage . On kill attributes are situational and counter intuitive . Healing ismuch more influential before the damage source is dead. I actually like hazard protection but it is too situational. Therefore , we are left with 1 health attribute on all gear, with the remaining attributes going to offense.