Y'all should forget open PK as a solution lmao. Cashers would rule the best spots while others who don't have dope EQ will eat ass. And you guys would end up here crying for another solution xD
Anti-KS system like i suggested is the only fair solution. It's basically who attacks first, owns the mobs.
From my experience it doesn't really matter what class, it's the human behind the character who is a sh*thead who decides to attack your mob pull. But mostly those turtles. Going SSJ, getting buffs and running around the entire Area one shotting the mobs and kill steals. If you farm, choose a f*cking spot and stay there to leave others a chance to farm too.