Right now, I'm using a grand total of 0 four-star cards in my Triple Triad decks. With how the deck composition rules are now, there's no reason to use any of them when you have five-star cards for the single "rare card" slot you're allowed.

It's a damn shame, because there are a lot of four-star cards, and it would offer a great deal more flexibility in creating decks if they were allowed in a less restrictive manner. Primal themed decks would benefit a lot especially, since there are a lot of four-star Primal cards. (Odin, Ramuh, Leviathan, Shiva, Ravana, Bismarck, Sephirot)

What I have in mind is perhaps something like this:
[1] 5* slot
[1] 4* slot
[3] 1-3* slot

At least that way four-star cards may finally have some use.