You could just make it so that discarding weaknesses put them on the bottom of your deck, that way he could use them for a benefit, but he couldn't just loop it forever. I guess what you did was a fine solution, and probably better, but I think mine would have offered more strategic options.
Seems to me that if you discard X number of cards, you only and must get a single card that has exactly X cost. The discarding no cards is not discarding any cards, so you don't trigger the effect and conversely if you do trigger the effect you can not take a starter/weakness card as they have cost zero and you must take a card with X cost which is not zero.
We will be using them for League Play before they get released, so "a while."
Ask your local store to inquire about a league with their distributor and get them early.
What is this "League Play" you speak of? I've been hoping to get something together like this as our local playgroup has lost some interest without any organized play. Has something been released describing the plan for "league play" for DB?
We will be revealing more about organized play very soon to all the DC Deck-Building fans and your LGS very soon. Everything will be revealed before the end of March. The promo cards first available during GenCin 2016 will be part of this initiative.