The TW system seems to be missing the most basic part of a usual matchmaking system. If a guild loses, match them against slightly weaker opponents next time. If they still lose, move them down a bit again until you get to a point where they win as much as they lose. Opposite for people who win a lot; keep making it harder until they're fighting equal opponents.
I would be amazed if I heard this system is actually used for TWs. So far for my guild we've lost far more than we've won, and the most recent TW was probably the worst loss we've had yet, despite following a string of much less absolute losses.