I haven't looked into this game beyond your description, but it does sound like a pretty weird model. Do you also have to pay for cards on top of that?
It's not a card game, it's an async autobattler. As long as all the characters are roughly balanced against each other, there's nothing to be gained other than cosmetics (at the current state of the game).
It's not copyright, it's patents...
(I do also hope that they lose because ingame mechanics being patented is bullshit)