Gravity is a unique sort of element. It seems to have a bit of everything, good creature control (Otyugh), good shield (Gravity Shield), good weapon (Titan), a way to get past shields (Momentum), and on top of this some very good Quantum Denial (Nymphs and Black Hole).
So, of course it will be hard for you to come up with a unique and balanced idea for an element which already has so much.
I also think the game needs more 'Rare' cards... Especially on the level of the weapon/squid/shard rarity... It seems to me, a little weird how we have 12 Rare Weapons and 5 Rare Other cards... then all of a sudden we get 12 Uber Rare Nymphs....