What the title says. I don't expect it to be 1 card every 2 games or something like that, but it could have some sort of hidden buff where the drop rate improves with a win streak. I defeated an NPC 40 times and I just go 2 cards... the same card twice! I still need the other 2 drops (yeah, I'm talking about THAT npc) and I'm scared I'll be stucked there forever.
I think the focus for the NPCs should be on their difficulty, not how bad the drop rates are.