I got both tiers first try:
1st tier (took less than 2 min):
targeted han and got kill, targeted chewie and c3po got kill, finished off with targeting ogchewie then cls.
2nd tier (7 min on auto): I'm not sure exactly what I did but I remeber ticking zam a little bit when could and mostly focusing bossk. After payout I set it to auto on bossk and was able to get kill at 50 or so armor shred stacks before focusing zam then dengar I didn't have much trouble with zam.
1st tier pheonix team seemed decently powerful with the assists and synergies with ezras 3rd and heras 2nd abilities.
2nd tier clone team doesn't really show that rex is bad in my opinion. It actually shows the opposite because he is facing a fairly strong toon (bossk), and two mediocre toons (zam and dengar) with a weak toon (clone sargent) and a mediocre toon (cody) meaning the match is:
weak, strong, medium, vs. strong, medium, medium.
So technically rex is hard carrying.
No wonder the battle is difficult.
I think that if you get up to 1000 armor shred stacks it should auto defeat the toon as part of scenario mechanics just to make it easier if you get dealt bad rng because no one wants to do a battle that lasts 4 or 5 hours for a marquee no matter the character.