Characters that give the debuff Daze and Stun do a great job at stopping CLS and the other rebels with counter attack. Like others have said Han Solo from the Rancor does great with his special ability stunning and his first attack dealing a high amount of critical damage. Your arena team could work if you be careful and avoid AOE attacks, unless they are under stealth from R2D2. Something to keep in mind you could try using Stormtrooper Han his taunt does great at giving the rest of your team turn meter.