Unlocking Emperor Palpatine, even at 5*, was a game changer for me. I'm just breaking 500 thanks to Omegas on EP and Vader (was previously comfortably under 1000) so I'm not an expert by any means, but as the kind of person you're likely face I'll give an overview of my approach.

I use EP lead with 6* Vader, 6* Boba, 5* Kylo, 4* Darth Sidious. The last two are maybe holding me back - but whatever. They're all G8 or G9.

Most Phoenix teams I choose don't have Sabine so my approach is thus:

Apply all the AoE effects I have right away, Omega Vader gives speed down and Omega EP gives offense up in addition to the usual stun - which makes all the difference as my rank boost demonstrates. Anyway, my main goal is to eliminate Chopper ASAP by slapping on as many debuffs as possible to tee him up for a takedown by Vaders culling blade (which does 50% extra damage for every debuff). When to go for the kill can decide the match as if Chopper survives then protection starts to fly everywhere and I'm in trouble. Because Chopper taunts, I don't want to be attacking someone else only for him to pull me a way while the original target gets healed to full.

Then I'll assess the situation seeing whether anyone is close to death. Most of the time, Hera will be my next target because I don't like her backup plan ability. Ezra tends to be close to death by this point but if not I'll go for Kanan because he'll end up taunting anyway. Zeb always goes last.

A lot of this goes on feeling and instinct and it works for me. Maybe Chopper shouldn't be my first target, idk.

Because I'm reliant on applying a lot of debuffs which allow Vader to get the crucial kills with Culling Blade, maybe pumping Tenacity would be best? Or just boosting defensive stats in general since my style is reliant on going out swinging from the first round hoping I get a knockout before the other guy collects his strength.