I'm in favor of a system where you can keep the drop rates as they are, but also add in an achievement as a buffer against having to win hundreds of games, like my 400-420 wins against Tataru T_T. For example, I can win Lightning card from Tataru with a 0.5% drop rate, or I can get it guaranteed after 200 wins against this NPC. If I am lucky, I win it on my 1st or 20th win, and then if I choose to, I can win the remainder and get a second from the achievement.