Unfortunately geo TB started breaking up amd reorganizing guilds on the higher end about a month ago similar to what HSTR did at first. I had to leave my guild to get over the HSTR hump unfortunately. At this point though most have been completing it for awhile.
You are correct in assuming this new TB will destroy a lot of good guilds and longer playing relationships as higher end members are forced to chase the rewards or be irrelevant in arena. Mid level and more casual guilds in the 130-170 mil gp range will mostly lose top gp members who were able to carry the guild through previous game play enhancements.