This is what I think I know about Galactic War:
Galactic War is supposed to be hard. I could not find the post to reference... There was an update and Devs said it is designed to challenge your roster to the fullest, not to guarantee that your roster should finish every day.
It takes a very deep roster for most to get through Galactic War.
As far as I can tell, you Galactic War nodes are based on your Arena Rank and/or Arena Team Power. I was ranked in the Top 30 for a while and completing Galactic War was very hard for me. The 6th node was a pain and often took out a couple bench characters before sending in my 2nd team. By the time I was at the 9th... it was pretty likely that I would be running out of character soon. Usually done at the 11th.
With the Palpatine coming up, focused on Rebels instead of my Arena team and my Arena ranking fell out of the top 50 and soon after out of the top 100. BUT I started to notice that with the addition of a strong Rebel squad... I started finishing Galactic War again.
So either Arena Rank, strong 2nd squad, or both made Galactic War easier.