Meer why only on this map? Make it the standard. It is too much that one can just leave the mob behind without trying to kill it and the one that actually kill it didnt get any.
First hit should be the standard for non MVP mob to get the loot, if the player leave the screen where the mob is the first hit flag is gone and is being given to the next player that hit the mob first.
For MVP of course it is the usual biggest DPS free for all (but also have same rule where if u leave the screen the biggest dps flag should be gone and be given to the next highest dps player)
Playing DoT-tele class should carry a risk that someone else might kill their mob and take their loots if they tele away from the mob if their first tick didnt kill them. They already have a safe leeway of only need to tele and use their skill and leave behind without having any risk of the mob targetting them.