Cutting Slash Resist by 20% is pretty broken too. Most people building for that have Iron Giant right now and it's only 15%. The game is already so bursty and this thing makes it that much harder. I think 10% ignore would have been plenty.
By the time this comes out a lot of people will be playing with pierce teams due to Glacia & Kain. I believe it's currently magic teams are the meta in JP. It's possible they added this card to help balance a few things out