It's actually fairly easy to build an unupgraded AI5 grinder. T50, not so much, oddly.
AI5 have lots of HP, but they're slow. Get a deck that has solid defenses and can get them up quickly, and combine it with healing to compensate for the HP difference, and you should be OK.
For example, since you like Gravity, once the new cards are patched in, you could try:
Mark of Gravity
9x Gravity Pillar
4x Aether Pillar
2x Quintessence
2x Lightning
5x Otyugh (Upgrade these first.)
4x Black Hole
3x Sapphire Charger
2x Gravity Shield
Keep your Black Holes until the AI5 has had a Quantum Pillar out for a while and has a variety of quantum; then it will give you maximum healing. Save Lightning to take a larger creature into Otyugh range if necessary. Use Otyugh to consume small creatures and Grav Shield to keep larger ones at bay. Quintessence one Otyugh ASAP, and then use the other on a Charger if you have solid control of the board, or another Oty if you don't.
Keep in mind that this is all off-the-cuff and untested.