Here's the obvious (to me) benefit to gravity:
0|1
Accretion: Destroy target permanent. Gain +0|15. When HP > 50, Activate black hole on both players. Your opponent heals from your quanta drained; you heal from your opponent's drained quanta. If your mark is Gravity, activate black hole on only your opponent.
Devastates rainbows, even if they try to use it, unless their mark is gravity. In which case, SoF satisfies its mark favoring. It even complements gravity by simulating a binary black hole system -- Focus.
(Under this scheme, you may be able to change its initial stats)