I'm sorry for the necropost, but i really think this is a nice suggestion.
Even without adding a text list, grouping cards would make the deck builder much less heavy on graphics.
And often i find myself counting cards in my deck (mostly pillars).
I also think it's really easy to implement, since this function already exists in "Your Cards" section (bottom of the screen).
I made a screenshot, just to be more clear about it.