One shot 7* Sid and lumi team in GW

Umm, that is a formidable team in Arena but once Poe's taunt is used up by the cannon fodder, RNG should get you out of there. As long as you have some good toons up to the mark, I don't see any impossible opponent.

Now if you don't want to use retreat multiple times or try different compositions to get the RNG gods on your side, nothing anyone can do. And I'm guessing you're pretty high level yourself seeing the opponents level (guessing cos GW match making is a black box and can be beeped up sometimes), you should be having at least 2 rows of usable toons. If you have concentrated only on 5 or 6 toons, GW will suck.

By the way, I faced such a team today in Arena. I knew it was a gamble and was hoping Poe wouldn't be in there, well he was and I was pretty much wiped out in the 1st round, lol. It was my last and only shot in trying to make it to the top 10 from 19. Lol, my gamble didn't work and was out of top 20 too, a few minutes later. But that's the meta right now...

Edit: Just in case, here's how I get ahead of teams like this. Send in my lvl 1 toon in alone, shaking in his boots. Once the taunt is thrown and the boots have been emptied, I send the other guys. Retreat if the RNG is against me, shake up a new squad or just change leader slot, go again. Haven't failed a GW yet not counting before I joined this forum.

As someone who runs the exact comp for arena maybe I can shed a few light. At level 66 that Poe probably goes first so your only chance is to have a dooku first turn stun or have your own Poe to out taunt his Poe. If you have QGJ you might be able to one shot the IG88 with a decent assist (~8000 hp or so). Again that comp is built around flooring at least one character and crippling half of your team within turn 1. You probably wont be able to clear it without casualty unless you hit some crazy RNG