To be fair, we all knew this could happen, just as any purchase of exclusive cards would also entail the risk of a possible balance change at a later date.
In addition, we should remember that this was primarily a Karn package, which included Gilded lotus as part of his basic deck. As such, any questions of refunds should fail, as we knew there was a risk of change, and because we still received the product advertised: Karn, along with his basic deck.
Furthermore, your purchase also gave you early access to those cards, and you got to use the pre-nerf gilded lotus for a prolonged period of time. As such, you got the immediate value you were promised, and the cards did exactly what you expected them to do prior to the purchase.
This is not a case of false advertising, nor was there any kind of promise that these cards would never be changed.
It is not a case of being promised a card down the line, and then receiving a different card; You got the +2 Gilded lotus upon purchase.
You got what you paid for, and ahead of purchase you knew that the cards were subject to possible balance changed. There are no actual grounds for claiming refunds.
Or do you want a full refund every single time a card or planeswalker is adjusted for the sake of balance?
When you purchase any card, do you seriously expect it to be set in stone for all eternity?
And yes, I usually don’t pay anything to play this game, and yes Gilded Lotus was the card that put the karn package over the top for me. But just like any average customer, i knew or should have known that it would likely be nerfed if it had turned out to be necessary.
Heck, even if it isn’t op, you are all fully aware that they might tweak the mana costs and effects of cards, especially regarding cards that you know are still undergoing testing.
D3 should not give a refund of any kind.
You knew what you paid for, you got exactly what you paid for and accepted the terms and risks. So complaints now are frankly just whining.