Here's my setup. Keep in mind that I'm only level 55 so none of my characters are anywhere near maxed.
Ackbar lead: gives my whole team of rebels a good amount of speed and tenacity, and when non-attack abilities are used lots of assists are called. Provides tactical genius which is especially useful for Lando, giving him back to back double downs. The dispel/heal is great too.
Scarif: super tanky with lots of health and protection, gives everyone turn meter on basic and buffs himself most of the time, AoE offense down/3-turn taunt takes the focus off squishy characters, gives everyone speed up when killed, and revives if killed while buffed (including taunt), which is almost always.
STH: turn meter generator with 3-turn taunt, but unfortunately I don't have him quite strong enough to fully utilize the taunt without him dying.
Lando: great AoE and lots of crits, resets double down cooldown frequently with multiple crits.
EE: good heal and cleanse, super useful for his revive (especially STH because he's always the first to die), but still a bit squishy so he needs to be protected by taunts.
My current strategy:
Stagger taunts between Scarif and STH so that EE is constantly protected. Let the enemy team wear Scarif down while keeping him buffed. Get him killed so he revives and gives everyone speed up. Use Ackbar's tactical genius mostly for Lando to crank out as much damage as possible. When STH or another character dies, revive with EE. If cooldowns allow, tactical genius can be used for EE to revive and heal right away.
This strategy is unusual because it basically involves killing people off. The tanks protect EE, who can revive them (especially STH because Scarif can self-revive) if they die. Meanwhile, Lando gets fed plenty of turn meter from STH, Scarif, and Ackbar's tactical genius.
The main issue with the strategy is that the AI doesn't quite work the same on defense and makes both Scarif and STH lead with their taunt, but overall it's pretty solid. I regularly place in the top 200 in arena and I'm getting top 100 more and more as I get stronger. I finish GW easily every day, only occasionally needing to swap out characters.
