Reverse Time's effect on a creature is, in some cases, bigger than other CC cards, but that's not the big issue: the problem is what it does
in addition to affecting a creature. It stalls. It not only gets rid of a creature and wastes quantum but wastes a draw as well. When used on your own creatures, it allows a deck to sidestep game mechanics and play much longer than it should be able to.
The CC can be considered balanced, sure, but it's the added stall component that makes it OP. Simply placing the card back in the hand first, deck second (if hand is full) makes RT much more balanced overall. Ghostmare wouldn't be affected much. (more in arena because AI is dumb with card play order - knowing the AI it'd play RT first then nightmare
) And self-stalls would still be possible, just more difficult to pull off. (this would be a good thing!)
As it stands, RT simply does too much. It just needs to be toned down a bit. What it does to a creature is okay. What it does to a deck at the same time, is where the problem lies.
Another possible suggestion: Delay creature 1 turn, then return to hand. Loses no CC functionality(in some cases it's better), loses the stall (usually)