Six Monsters low-diff or stomp under these conditions. Giving Gajeel DF and Mira unlimited Alegria is pretty unfair tbh, this would have been a debatable match without giving them that advantage.
Pretty much the only thing that lets CS stand a chance here is teamwork + Jellal, but Jellal isn't enough to 2 vs 1 DF Gajeel and Alegria Mira. Hell, some people on this site would say he would lose to either of them, let alone both at the same time. As for the teamwork, while good it means nothing since once Jellal goes down, Mira and Gajeel can just clean up.
Also why replace Levy with Juvia? She's a good support mage and makes the match a little more balanced (or less depending on how you rate Levy vs Juvia lol).