you should be able to do it at that level, thrawn isn't like palp you can't just power through it by sheer force.
a few things that will help will be mods with speed, getting your abiliites as high as you can, and the right strategy:
first 3 phases you should only use normal attacks to built up offense bonuses and keep your abilities ready gong into phase 4. rng also plays a role as you will want either chopper or ezra with 90% TM to debuff ST immediately and kanan with 90% to taunt immediately to soak up that fracture.
I found it works best to focus on thrawn when fracture is not up, use hera and ezra to get in extra attacks by zeb to keep him stunned and force him to waste turns on getting rid of debuffs. when fracture is up take out those death troopers, then the commanders, then ST. I just finished it on 7* using this strategy. ended up killing both of the death troopers (one committed suicide by AOE) first and had thrawn's protection down, then switched hera's assist to ezra and powered thrawn down quick. Lost kanan during the fight (irony), but it was a relatively easy and controlled battle.
