To preface this discussion, the empire uses suppression and debuffing to grind down their opponents. The last leg of the R2 event prevents any turn meter reductions, so you're already at a severe disadvantage, especially if using a Vader or Zader led team. R2 and Han provide most of the buffs to the rebel team, with tanks chewie and Ben grinding, and leia and Luke shooting up everyone. On top of all that, your turns come slowly at the beginning and only after r2 has gone insane on you. If you are going insane trying to beat this and just can't no matter what you do, the answer would be the Tie Pilot, especially if you have a sub par enpire team. He prevents buffs with tie strike, and can cause considerable damage to those characters with debuffs with his pistol. He also has a chance to get foresight, which helps out a lot, especially if he's low gear level. I'd recommend him be at least GL8. My team consisted of Tarkin lead, with Vader, Royal guard, and snowtrooper. A good strategy would be to use tie strike right out the gate and prevent any stealth or buffs on anyone that's affected. If tie strike is completely levelled up, you can try using it on R2 primarily and hope for an ability lock while getting buff lock on at least 2 or 3 other toons. Try hitting leia and Luke or han first, taking out a huge area of their attack. My particular team was huge with AoE so it whittled down a lot of energy. After softening the rebels up, throw all you got at R2 because he is a **** to take out. The tie pilot was great here as a pistol strike on a debuffed toon potentially does a lot of damage. Also, if tarkin is your lead once the protection is gone on any toon, you got expose on them for massive hits. After R2 is gone, you have Ben and chewie to deal with, but that's just a grind. Honestly, if your tie pilot survives the opening salvo with at least 10% of his protection intact, chances are you'll make it and then be ready for commander Luke, who btw is VERY easy to obtain in his event.
Guys, I hope this works for you because I know how horrible the r2 event is. If I explained anything inadequately, please let me know. This is from my personal experience and I'm hoping you are successful with my advice because CLS is absolutely devastating. I used to hover around 900s in arena, and now I am currently 324. Good luck!