Apologies. One had tried to be as concise as possible. I will specify the exact loss.
Here is the transcript. I also increased the maximum cost, in light of your valid assumption zero cost cards in hand would derive a greater benefit. While not as you commented:
War Council. Uncommon. Zero-Cost.
Lose up to 4 resources for each card in hand, based on cost(no more than card cost)
Gain random Tower, Wall and Stock until total gain is 15
Now, as I can hope I've conveyed, zero-cost and low cost cards in hand can net you benefit, while a hand full of higher cost cards will cost 32 resources for a paltry gain. A gem cost card would cost you up to 4 gems, while a Miracle or Priest would only cost 1 gem, an Oasis 3, and on and forth. mixed-cost cards with all resources mixed would up to four of anything, not four of everything etc.
I hope the card now describes the effect as intended?
In the original, Zero-cost card benefit was only an afterthought, but, now the idea is you wait until your hand fills with low cost cards to play War council, and receive a random but cost effective gain.