I have had this situation as well, and some of the issue seemed to be weapon / spell set up.
I personally have a Deepsky stone (125 lifetap) and Baubble of Agression (+4 Fire Dmg) (listed just in case someone did not know

) I am constantly stunning a mob when I have aggro, switching between Sacred Force and Ancient, and had issues with a SK taking aggro from me. I ALWAYS use epic 2.0, unless I am tanking a 4k hitter. Depending if the SK religiously uses and then aug their epic with Enraging Blow and Chaotic Strike 4 (which the SK in my scenario had) aggro can be an issue without necessarily trying. Not only are they swinging a little faster, but the procs are pure hate with the added modifier from Voice to the procs and each swing.
Mind you, I agree completely with you, and if someone takes aggro, fine, have it, and I look for the next mob that is not locked down. I personally would rather take a mob off a Druid, Wizard, Mage, or other silk class / healer than fight for aggro. Hell, I could care less if a Ranger or Bst OTs a mob. That actually does happen during our raids as they also would rather tank the mob, and have the ability to, compared to some other classes on trash.