Wow so many kitten posts.... "I hit auto and win" is probably the closest indication of a lie.
Either way, here's my advice for you bud: firstly, a good indicator for this event is Palpatine's event - if you are able to clear it, you should at least be arriving on the final stage of Tier I. From then on, if your goal is not focusing on Rebels (mine wasn't), it's a matter of trial and error until you get the gear and mods high enough to clear both Tiers.
Just keep upgrading them one by one and see the difference it makes in your fight. For example: you have a Rebel team full of 7* Gear 7 toons. Didn't finish? Get your best rebel toon to Gear 8, then try again. And so forth.
I finished with Wiggs G9 (L), CLS G11, Biggs G9, Ezra G11 and R2 (Gear 9).
As others pointed out, just try to put a stun on Palp before the RGs taunt - after they do, hit them hard and pray Palp doesn't take out your strongest toon.
But the best advice is to upgrade gear level on toons, and again, if your focus isnt rebels, just upgrade 1 by 1.
Hope it helped!