I looked at the changes and I have to agree. Even Akebono uses armagios often for overdrives and he should have enough quanta.
The problem is, technically you don't have a leg to stand on.
8 attack = 8
Over 10 HP = 3
For a combined cost of 11
Most upgraded cards get a slight break, but again, 30 HP isn't just a bit over 10, it's triple the value. You can't make it too extreme, if it had 100 HP then gravity force is another life bar.
Honestly, I am starting to hate these things, because already you can barely kill them. Maybe some wacky effect that's not OP could make people play it
1) The graviton guard starts to be a useful card and produces lots of gravity quantas for the dragon.
2) The graviton guard can mount (only!) the dragon to create a powerful dragon rider.
Solves 2 problems at once