Agreed. The nymphs are not game-breaking and are really more of a novelty since you can buy any of their abilities as a spell card. It's nice to have one and it'd be nicer to have more, but how many anti-FG decks or T50 decks do you see out there?
I actually find it a luxury to have "novelty" cards that aren't used in any decks in a card game with only 10-12 cards per element.
That's like saying
"yeah we know the game needs at least 3-5 times as many cards as soon as possible, but look, now we'll add 12 new cards, which is 10% of all the cards in the game, and we'll make them both unobtainable in the game normally, and also not too useful otherwise the rarity might become a problem...that's it for new cards this time guys, but look, we got 5 more false gods added to make the game even harder. Good luck! What? You want to change your account's password? We won't implement such an advanced feature this fast, the game has only been around for a year, you know, no need to hurry..., we'll add new features later, don't worry we made grinding hard and slow enough so you will have stuff to do until that happens hehehe
"
I know this is not what the developer intends, but it is what the players, including myself, experience, and that will be very bad for the game on long term. Anyone who has anything else to play or do just quits after he realizes how boring and frustrating the game became.
I seriously consider just giving up and replaying some yugioh game instead. Even that is more interesting, and fun than this.