I don't see why cards need to be quite that simple. I generally take about 10-15 seconds for reviewing each card. A lot of my cards are why/how/what questions (typical examples: "Why are bras covariant?"/"How are Green's functions used in solving linear differential equations?"/"What is Q-Learning?") The problem with skipping memorization of concepts after having understood something is that two months later, you'll have forgotten those concepts. So, all that effort will have been in vain. I typically don't create much more than 10 cards a day, or maybe 20 on a day where I'm taking in a lot of information, and I typically have less than 50 cards to review. It's really not a huge time investment - especially if you're "busy".