This card double dips on too many fronts and I'm not really sure what they were thinking when it was designed. First, it is removal that isn't based on dealing damage so the better the creature your opponent plays the better the value. That's OK, plenty of removal cards like that but it isn't just removal.
Getting your opponents creature is absurd card and mana advantage. Your opponent spent at least 1 card and some mana to play that creature and you are spending 1 card to not only remove it but also get it. That's a 2 card advantage but more realistically could be much greater as cards could have been spent to buff the creature and\or your opponent may need to spend cards to remove it. Mana also scales absurdly as the higher cost the creature you control the more efficient it is. Subtract the cost of removal and it is easy see that this card is far and away a mana advantage even at the nerfed cost when used on late-game creatures.
All of that said doesn't even touch upon the board control advantage of -1\+1 being a silly powerful shift. I'd like to know what other cards exist that shift board control to such a degree.
I just don't think the problem with the balance here can be fixed by adjusting the cost. I think the card is very poorly designed and not fun. Discussion about how the class does in competitive play or any level isn't relevant. In a game that is based too much on RNG at the expense of skill I don't think cards that are designed to be this cheesy have a place.