Completely out of the context of this thread, I wanted to point out that bad cards are still interesting for casual players which do not know how bad they are. If their effect is interesting, people can still have fun while not caring that much for competitiveness. I had a lot of fun with thief for example, before discovering he was bad. A few of such cards, could exist in every set and they could be excluded from random online play, unless people decided to include those cards in their game purposefully.
It is possible of course that a card has an interesting effect and attracts casual players as well. But still it looks like there is room to create cards that would appeal more to casual players, without hurting the core target group of dominion players.