As far as I am aware, Guild War matchmaking is supposed to put your guild against a guild with a similar number of people ONLINE at the time.
Came across this guild in Guild War, turns out these guys are having their members log out so they can get GvG matches against lower number guilds and then having their members log back in to fill all the slots.
When they first joined, they had 15 people, which was pretty much matched to us, which is fine, normal matchmaking, then it suddenly jumps to 27 a minute later with everyone who logged back in.
Messaged their leader and he was responsive and talking till I questioned him about the exploit, then he immediately stopped responding.
Vice Lead, Krissa, DMed me in game after the initial post, also deflecting the question about abusing the log off, log back in mech to get matches against smaller guilds. Pretty much confirmed it afterwards as seen above.
Maybe it's a part of the game that allows guilds to mass log out and then back in to go against smaller groups that some choose to exploit, but those who do abuse it are cheap asf.
Devs need to fix this shit.