I find it weird that you chose to go with 3 whole decks of cards, rather than sticking with just 1 deck of cards but 3 different deck layers. Let me explain (if this has been suggested before, sorry, just consider this post a +1 xD):
Basically you allow the players to put all the 12 stats on the cards (11 normal stats + the bonus all attributes stat) but force them to only choose 4 stats per deck layer.
Implementation shouldn't be that difficult, because each deck layer will be just a simple filter where players can filter which 4 stats they want to have in that layer...
It's still a horrible, expensive solution (unless you make it less expensive & less rng based) but at the very least, people won't have to farm ridiculous amount of cards. You do realize that these cards don't drop easily, right? By the time most people manage to farm just one full deck, they will be grey and in their 80s!
Not exactly the legacy most people want to leave behind...