Arcane has several advantages:

* Missiles are not interrupted. So all Mages always are at the same step of cast canalization. (excuse my english)

* Since they canalize, all mages turn their direction if a mob is passing by. With fire or frost I have to rearrange the mages per "follow" first.

* It starts instant and saves time. Normaly I have a mob down with arcane missiles bevor the first fireball would have reached him.

* A casting mob who recieves an arcane missile every 250 milliseconds has more trouble to canalize his own cast.

* Since I'm specified on arcane explosion, arcane missiles profit from my arcane tree talents.

Nevertheless:
* in the video I could have get the 2. boss down much faster with ice bolts.
But it would not have looked so cool ;-)

Greetings:
Sciva