And why not? It's like a lot of other AoE cards (although this does admittedly get "weaker" as the range gets smaller).
>Play against most decks, nothing happens.
>Play against that one gravity deck every once in a while, SUDDENLY YOU LOSE TO WHAT THE HELL WAS THAT
>Play against that other gravity deck every once in a while, it's suddenly screwed over because of random massive HP debuff.
Its -5 on the opponent either causes you to die a WTF fast death, or magically screws over your opponent just because... Magic.
I don't think either result is fair on either player.