But the point is that the playstyles in Overwatch SHOULD be the heroes themselves. Sure, you can be aggressive and defensive as a Reinhardt, but the core strategy of taking space with the shield and knowing when to attack/defend is vital in the games balance. We’ve already had major issues with balance being off kilter with even the slightest buff and nerf given the team aspect of the game, and to add a cards system on top of it? Imagine if Brig got a buff where here passive healing when up with her Inspire. Some situations would be a nightmare.
The fact is, the way that the game balances heroes and at the rate it does, a cards system would be horrific for the game. It works for paladins, but it wouldn’t work here.