Matchmaking is based on overall guild GP.
For longer than 6 months my guild has had an over 90% participation in these wars. I know this because I keep track and kick anyone missing too many. But every single time we have been paired against guilds that not only have a heavy per player GP advantage, they have players who have Galactic Legends characters and SLKR.
Not one person in my guild has SLKR or even close to getting anywhere near a galactic legend. Personally it will take me over another year before I can get close to what I want.
We are guaranteed to lose based on a matchmaking system that favors power over equality. Matchmaking should be based on an average of all guild members GP. There are way too many veteran guilds exploiting the system by keeping their player numbers low to keep their GP low so it's a guaranteed win for them every time. Anyone who says otherwise is either a liar or benefiting from the current system.
This screenshot shows what it has been like for our guild every single war. I am seriously fed up because our guild participation couldn't be better with every territory filled up.
1 win in 6 months is not acceptable odds.