I think it is normal that you can not beat GW during a specific phase of the game - mainly when you are close to 85 or fresh 85. You have put most effort in your arena team, got your first zeta and no backup. Just accept that you cant beat GW during this stage of the game.
There were 1-2 months were I almost never finished GW. After that, my rooster had improved and I had invested in the right toons to beat the unbeatable squads (mostly Nihilus, Zylo and Zarris). Then there was the time where I had the most fun in GW - I got all the current meta Trawn-Nihilus-Kenobi squads in node 12 that were really, really hard to beat. I only had six good toons and tried a lot to get the right composition and strategy to beat these teams.
Now my node 12 is broken and the fun is gone. It has become too easy.
Moreover, don't expect to beat GW with a pure damage squad (like Wiggs, Lando, Boba). GW is all about control.