The only strategy that works against RG is play with Poggle as leader, then with Geonosian Soldier and IG-86, thanks to Poggle, GS have +25% offense and a lot of times will kill Rey or QGJ at the beginning, and then use Poe to reduce the turn meters and with IG-86 (with offense up and Poggle as leader is +75% damage) kill RG. The 5th character can be another attacker, as IG-88, Rey or QGJ (not as leader), or Resistance Pilot or also HK-47 can be useful, but not as leader, because GS need the leader ability of Poggle.
I have RG and Poe in the same team, and the strategy it's the same, kill my IG-86 at the beginning, and then kill RG, kill Poe, and then GS and Poggle, but it's not easy, this night I only lost 7 positions, I only needed 2 battles to go back to the 1th position:
https://www.youtube.com/watch?v=hYvzJjtrC9g
https://www.youtube.com/watch?v=24vdPnKg26E