Yes but Archbishop was a title for the leader in the Cathedral of Light. If Velen was to attain the title he'd need to be in the Cathedral doing whatever the Archbishop does.
Id be pretty pissed if I had to travel to the other side of the world just to attend lectures from some Archbishop who doesn't even believe in the same "Light" as I did.
Draenei believe in the Naaru, Humans and Dwarves believe in the "Holy Light". Sure the Naaru may be an entity of light but that doesnt make them the same thing.
That Bishop would still need to travel the world just to answer to Velen, which I wouldn't be fond of doing after the first few trips.