The casting and interrupting of the Mage LB is a CC in itself. Most players run out of a circle when they see it appear on the ground, running from their targets. Thats why its nerfed and half when interrupted, it can, and is, used a an AoE CC. Adding a cooldown will allow this CC use of the LB once again.

I run FL as a SMN and I used it as CC then interrupting its cast. I know I'm not the only mage that does it.