I can't even begin to think how you would manage to play with the priest main remote controlling a warrior. What happens when a mob adds on the group? The warrior needs to run over and taunt it. Even PvP, I would always control the melee character over ranged characters purely because the melee character is always moving while the ranged are staying put for the most part. For melee the target must be in melee range and they must be facing it, for ranged the target needs to be out there in front of them somewhere.

What does the priest have to do? Heal. Dispel Magic.

What does the warrior have to do? Sunders, damage abilities, positioning, taunt, shield block, shield slam, etc etc etc.

But purely from a positioning perspective I don't even want to think how difficult it would be to do from a perspective other than the tank's.