Gravity needs something else I think. Consider the 3 healers' aoe spells:

WHM
Holy: Moderate Damage, big radius, can be used consecutively to inflict up to 6 seconds of Stun, has the same cast/recast so cannot weave/move during the GCD.


AST
Gravity: Low damage, small radius, has a fast cast so can move/weave.


SCH
Art of War: High damage, small radius, instant cast so can move while using.

I think Gravity needs maybe a Slow effect added to it (say 20% for 10s,5s,3s,1s roughly on par with Stun?) to justify that it's the weakest potency of the 3, doesn't have a debuff, yet still has a cast time.