I think the fact that it takes up to three turns to work its "magic" balances out the fact that it can commandeer creatures. It gives the opponent enough time to counter it, and the repeated usage of gravity quanta would be hard to sustain in the meantime. The "one turn" situation (where the enemy creature is in the row closest to your field) would only occur with swarms of creature such as Fractal decks, Queens, or Pharaohs (or SoSebows, which can multiply fast) and by that point I think it would be safe to say anything you do wouldn't compare to the damage output on their side.
That said, I intend to lower the HP and/or raise the casting cost to make it harder to pull off successfully. I think the ability cost can stay the same, considering only Entropy Nymph has a costlier ability (unless I'm forgetting some).