Also, mobs are difficult to hit when they are right next to someone, or possibly in that person. Your cursor seems to prioritize targeting your ally over your enemy. It would be nice if there was a Key press + Click that would allow you to set it to focus Enemy vs Non-enemy.
Default: left click is to focus on Non-enemy (other players in or out of your party).
Shift + Left click = Focus On enemy targets under your cursor
Ctrl + Left click = Focus on Party members under your cursor
Alt + Left click = Focus on Any non-enemy under your cursor