As I understand it, the S+ cards on epic used to give the bonus stats (the ones in blue) but not the base stats themselves. As a result, you may have gotten a few extra attack/defense levels, but you would have lost out on all of the base stats, and the lack of max spirit could really be a disadvantage in pvp. Now, the S+ cards have their base stats reenabled, and have extra bonus stats to boot, which essentially makes them the all around go to choice.