Well I got in about 30 tries over my lunch break focusing on Rex only first. Still havent come close to beating it and was once able to get both Rex and Ashoka downed with all 5 of my starters still up but reinforcements back to back using high damage specials quickly took me down to 2 active ships and from there i could not reinforce fast enough to spread the damage around. So I was eliminated with 3 ships in reserve that were basically useless.
If my ships dont surive the initial barrage, I retreat and start over. that was about half of the battles. On the others using a starting 5 of Biggs, Cassian and fives for guarenteed TL, JC and Ashoka my typical fight would get me taunt and decent purple protection on Biggs while Rex was either killed or very close to dying. Then enemy Ashoka cleanses my Biggs taunt and protection and by the time I can get to Cassian to TL again to get taunt someone was already focused down or the taunt train had started and I end up killing no one.
I plan to keep going at it but as others have said, the strategy is only as good as the RNG allows it to be.