Would you want to play PvP in game where a class like archer could endless kite an opponent by using the shadow bind combo, binding a player in place then continuing to pelt a player before bind wears before resuming the kite chase. Or what about a Thaumaturge inside a closed instance that is capable of striking anything within a large radius well outside the range of any melee class. It would also have the added benefit of not having to build TP or engage active mode.

The classes/jobs in the game are designed for specific roles. It's why you are able to swap our class/job at almost anytime. So any player can fill that role by changing it's class.