Thrawn tier 6 is completable with level 63 - 66, gear 8 toons. I didn't use Sabine -- don't have her to 6* yet -- but the rest worked well, and maybe even be what the event was tuned for with Chopper's extra taunt and extra buff cleanse.
I must note, however, that I had to put top arena level mods on them to make it work. Really, I think it was more of a speed thing than anything, as the more turns these guys get, the more they heal themselves, can provide protection up, or can stagger and offense down the enemy.
Following the strategy tips above will get you through phases 1 - 3. I entered phase 4 with full health and most of my protection remaining.
Phase 4 Strategy:
The Deathtroopers are your biggest threat; the stormtrooper in the back is not, but he taunts and auto-taunts and starts with crit immunity. Your first task is to cleanse the taunt from the stormtrooper with Ezra or Chopper. When cleansed, he'll taunt again, so be ready with Ezra or Chopper to cleanse the taunt again.
Your next focus is the Deathtrooper on the right. He starts with a buff that I didn't read entirely, but it gives himself 100% crit chance among other things, it looked like. That buff can be cleansed with a stagger, so stagger him with Zeb when you can.
Bonus in this tier is if you hit your enemies with debuffs, they may take a turn to use Thrawn's leader ability and cleanse themselves. You might find this annoying, but it could mean less incoming damage.
The tactics above are all background to keeping your team alive. Never leave a man behind. Apply Backup Plan to whoever gets Fractured by Thrawn. This will help heal them when they're past Fracture, and revive them if they get taken out. You can't apply more buffs on a Fractured character, so leave the Backup Plan on them and get protection up on others with Zeb and Kanan. If you're able to taunt with Kanan, do so and pile the protection up on him.
Remember, Ezra's Watch and Learn special can give a tank protection up, so use it on Kanan when he's taunting to keep him alive. Kanan's first special can cleanse another ally of debuffs and his second special cleanses himself. Use them to dispel Healing Immunity from your characters. With Chopper and Zeb, each turn they should be healing protection and health.
For my run, I saved Thrawn for last. Focus on taking down the Deathtroopers first; they're your biggest threat. Then the stormtrooper way on the left, then the taunting stormtrooper in the back. If you have all five characters by the time you face Thrawn he should be pretty easy to take down.
Again, I piled my arena mods on these guys to accomplish this. My Phoenix is only level 66, gear 8, 6*. I tried 3 times first with lesser mods and it just wasn't cutting it. I could barely break them at all. Hera I got to 222 speed, Ezra 200 with 216% crit damage, and Kanan I think had about 20k protection and 15k health. This may not be possible to achieve at level 66 gear 8 for everyone.
