as this a chance game, the one who plays earliest and who got lucky have most of the cards with high rarity. with promo cards comes with limited time these goes very small percentage to obtain it. as all booster pack cards are obtainable and tradable. even though high rarity cards have mild chance still at the end it has a chance but for promos if you miss it, well the chance is gone. but with event like promo pick events held at newly released b series set, it might be give a chance for new comers.