I recommend not playing this game until the developer has released good free2play decks and Book of moon in gem access.
Playing ranked right now with free2play Harpies or Blue eyes is means that Resonators, Gaia and Thunderdragons will wipe the floor with you.
Let them play against each other, don't let them easily rank up
Many people reach KoG with f2p decks like Triamids, Gouki, Hero, Magnet Warrior, Witchcrafter, U.A., Satellarknight, etc. If you can't reach KoG then it is basically your own problem.
If it's nothing special why people buy 3 copies of Book of the moon for $200. I saw the guy with the prismatic book of moon in ranked I don't think this is an esportsman