This is not a complete answer, but this is a very important point when it comes to designing games.
It is vital for a TCG or CCG that cards have varying power level. There have to be some completely awesome cards (without being broken, like
SftF,
CbtR) and there have to be some terrible cards that are never (or almost never) worth playing. The main reason for this is because then it allows the game to very easily differentiate good players and bad players - the better players know what cards are good, so they use those to build their decks while the bad players might consider the bad cards better than they ought (for example, when I first saw
SftF, I thought it was terrible!

).
There's also another more obvious reason: without the bad cards, you have no way of judging how good a card is. The fact that there are good and bad cards puts them into context.
Thranduil