7* Thrawn with G9 and G8 Phoenix Squadron

I can vouch for the OP. I tried with arena-level mods and G8 toons (I also have to use Chopper instead of Sabine). Hera was my only G9. I didn't come close, could only down one enemy in phase 4, I tried 3 times, same results. The I upgraded Ezra to G9 and I managed to down everyone except Thrawn and one other toon. The difference with G9 with just Ezra made a huge difference.

I managed to down Thrawn after adding Omega to uniques for all except chopper. I also added a couple more gear pieces to Kana. So final tally:

Hera G9
Ezra G9
Zeb G8
Kanan G8
Chopper G8

Also Zeb stun and daze is absolutely critical to winning