Speed Rainbows (~30 cards) are the most popular current deck. They are good at PvP - since most players see a Rainbow and expect a Stalling variety such as ScaredGirls. They can pretty much dominate the Top50, since a human mind is invariably greater than the AI controlling the T50 player's deck. And, against False God's they don't fare too badly, all down to lucky draws etc.
I would hazard a guess that Zanzarino is heading towards us storing up to 3 decks, and arming ourselves with our chosen deck before going in to battle. Instead of manually removing all cards, and then tediously adding the ones you want in your new deck.