2 damage for discord? That's way too much. Just because it's effective against mono decks doesn't mean it's OP. If that's the case, then BH is OP because it beats rainbow decks and RoF is OP because it beats fractal decks. Just because a card has the chance to be effective against a certain type of deck doesn't make it OP.
6 cost for a 4 atk weapon is insanely UP. It would become completely useless. It's usefulness will become around dagger's in terms of effectiveness. That's right, almost 0.
Now back to 3 cost for 2 damage. Just think about it for a second and you'll realize how big of a nerf this is. Arsenic comes to mind? Yes, 2 cost, 2 damage, increases each turn. Fahrenheit, 3 cost, 4+ damage. Druidic staff, 2 cost, 2 damage, heal 5. Vampire dagger, 1 cost, 4 damage, vampire.
I think that's enough examples for now. Now, take a look at the weapons that I mentioned. They're useful in every situation, while discord is useful only like 50% (4 types: mono, duo, trio, rainbow). It also depends on the deck's type. If it's a stall deck, discord won't even matter, since sanctuary will almost 100% of the time be there.
There is no way to nerf this card without making it almost completely useless. And as it's already been stated, discord was already nerfed.