Well you can't just use all good ninjas. If you make a team with 3 good ninjas, that team will disappear once you won with it and then you're left with 2 other teams with garbage ninjas in it. You have to balance it out each team you are making and win with every single ninja you picked at the beginning.

In summary: Zenith has literally nothing to do with coupons/ingots outside of getting Sage of Six Paths rank in Ranked Arena to participate