Meh, fair. I think I was automatically assuming that this was a decision made after Neltharion's corruption, whereas it would actually make a great deal of sense if they were intended to subjugate the mortal races and preempt any further defiance of the Aspects.
I would add, however, that I think they probably would be useful in disposing of the Primal Incarnates because a swarm of smaller animals with a great deal of offensive power can be pretty excellent in killing larger prey.