Some possible minor improvements:

When allies of the tower-holding guild attack the flag, there should be no change.

If there are two guilds in a guild spar, one with two members and one with five members, only two members of the five-man guild should be randomly chosen to spar. There is no purpose in having unequal teams facing off. However, in a GST setting, if you don't have five people, you should have to spar at a deficit.