You have to less lvl 60 champs to replace anybody. In addition to that, I don't see a champ that (levelled up to 60) and joining your team would bring an astronomical difference. I guess 10 million per key is the maximum you can achieve right now. 

Level up your rearguard sergeant to lvl 60 and visit the minotaur to give all champs in your CB-team Warmaster/Giantslayer mastrie will increase your damage.

On the enxt step, you could say that Tayrel is redundant to your team. Def debuff comes from Ninja allready, Rearguard has atk debuff. I think Grush could join, leech is a very strong way to heal your team, as the champs can heal from the damage done by Warmaster/Giantslayer and get full health immediately that way, if the masterie procs. But you can't do that change right now, because Tayrel is lvl 60 and Grush not. Replacing a lvl 60 champ with a lower rank will reduce your damage.

The artifacts of your Klodd are terrible. The shield set is just wrong for CB, a protection for the first 3 turns and no effect after that doesn't help, it's a set made for short fights (certain arena teams can use it). But not only the set, even the stats are just wrong. Klodd should have accuracy to land his decrease critrate debuff from the A1. The critchance of the Clanboss is only 15%, if you land the debuff, he can never crit (very underrated debuff for CB by the way). The accuracy should be 200+ for nightmare CB, not only for Klodd, but for everybody who is supposed to land debuffs. 

/edit: Using Klodd 150 acc from artifacts are enough, as he can increase acc.

drop tayrel and klodd and replace them with rugnor and giscard. get both of them up to rank 6 and eqipped with warmaster mastery asap. rearguard seargent should also be replaced, but she's doing the most to keep your team alive so she's a lower priority to replace. vrask could do the job if you don't pull any better options between now and when you replace rearguard.

You might want to consider dropping Kael for Ghrush. That'll allow you to swap out lifesteal on your champs, since Ghrush can keep leech up constantly.