I've been using a 7* GG for nearly six months and sit comfortably in the top 5 on my shard. I had an issue when the Wiggs/Lando meta turned up and Rex leads still give me trouble but all told, I don't slip much on defense. I have all droids, all maxed (except Omega on 88's basic) and have tried a lot of different loadouts.
I run two variations:
HK, GG, 88, B2, JE - this has been consistently good for me, especially against RG+STHan teams. It's the team I most often leave for defense. One point to note is that B2 can output some of the highest damage in your team. Individually his shots look weak but he can potentially fire 5 blasts in the time it takes one enemy toon to go twice. There's a vid of him in action at the bottom of this post. He starts off pretty badly, as does GG with an early stun. But once he gets going, he's a monster.
HK, GG, 88, 86, JE - I've had to bring 86 out of retirement to give my team the ability to delete Lando or Palpy early. I use this variant if the enemy has only a single tank (even better if it's STHan and not RG), unless that tank's Fun Sac.
The third variant I had months of success with was HK, GG, 100, B2, JE. This is a great team for grinding out evasion or Phasma leads if there are still any left on your shard or if they start turning up when the level race starts again.
https://youtu.be/UWp1jI8n0p8