Powerful is for an exaggerated effect or attributes.
Causing something that is damaging you and healing a foe, to damage the foe and heal you, is a very large effect, literally at least twice that of killing it. Its steal for creatures, destroying the creature on the opponents side, and putting it on your side, except it doesn't do that, so is immune to shields too. Something with 13 damage, would have the effective of 26 HP difference each turn when using antimatter on it.
Using antimatter, on a antimattered creature, has that same large effect, its still the difference of 26 HP each turn. Using antimatter to reverse antimatter is a exaggerated effect as well.
Reverse time only effectively kills pumped creatures such as chimera, pumped lava golem, pumped otyugh, etc. It slows down the opponent but doesn't takes out a creature he/she can use,
If someone kills a creature, it costs a opponent the mana cost of the creature, it costs a card, and any effects on the creature. One can place down a new creature to replace it, even a identical one, but those costs are not directly recoverable.
Reverse time has exactly the same costs on the player it's used against. Except it means that the next card drawn is the creature killed, rather then another random card you might need. (like a piller for energy needed to place a creature again, or a shield to save you from a row of attacking creatures)
So the difference between killing a creature, and rewinding it, is minor at best.
Antimatter only kills effectively high attack creatures without immaterial, lobotomize only kills effectively creature abilities without immaterial, yours effectively kills ANY creature without immaterial. Yup, yours still more powerful+flexible.
A card to kill any creature is more flexible, but notably less powerful then antimatter and lobotomy. Yes it can do both, but does so much less. Antimatter has twice the effect, and lobotomize has affordable repeatability. Antimatter even has affordable repeatability on a nymph.
I'm very happy you made a new version. It has my approval (even if it doesn't means anything).
You might consider putting your approval there, it would be more likely to mean something there.