Whereas a card to selectively discard from your opponent's hand might be more useful in some cases, this would be more useful in Hidden match decks. Having a card in hand with which you choose which card to remove from the other player's hand generally isn't worth the cost in Hidden matches, and even if the opponent has a Durable card being put to great use, its location can be effectively masked by quickly playing Quick and Swift cards in the same turn, causing your opponent to have to keep close watch or guess.
It would also be useful in clearing Durable cards from your own hand if it comes to it, though admittedly not as useful as existing self mass-discard options.
Mostly, I wanted a stronger Banish since the keyword is still terribly useless against the fourteen Rare Durables, the three expensive Banish A's notwithstanding. I suppose I could lower the cost since the self-discard would possibly be a detriment more often than a benefit. Oh, and yes, the Banish keyword is intentionally redundant.