More play cards work
Updates to the card fights are in progress. Play cards can now be obtained in exchange for permanent stats. Play cards can be traded and auctioned too. The price of a card grows based on how many cards you already got, so the first cards are the cheapest, but the order is decided by you. What makes players different when it comes to play cars, are their choices, and their number of total cards they hold.

You have no restrictions on how many play cards you can hold, so you can get more via trading.

Pending updates: The card fights mode will no longer consider stats, but just strategy. Strategy is influenced by strategy cards, so in a way stats influence battles even in cards mode, but weaker players still have a chance just by using a better strategy.
The old fighting way remains. I noticed you are just using it to farm stats, so as far as gameplay and strategy goes, its useless and can be replaced by easier ways to farm stuff, if thats what you all want/need.

Its not a good time to get these cards in exchange for permanent stats, lots of variables still to be decided, and i won't refund your decisions, better wait for me announcing its complete, or get them on your own risk