I'm under the impression guilds will be matched up based on how they have been doing ("paired against a similarly ranked guild"). The Archibald(7*) reward is based on win count, so win count seems to be a high priority.
To maximize win count, could players (with teams of 6*s) drop their guilds towards the later matches (avoiding the tougher battles) and join terrible guilds that will have easy match-ups for the rest of the way? Wouldn't this make getting wins easier, and therefore make getting the 7* reward easier?
Would this work?