I think there is an cause for concern that a guild with 2 mega whales that have 6 mil in total GP, could effectively beat a guild with 50 members at 600k, The 600k guild would be drastically out manned in probably both the amount of g11/12 toons, but mods as well.
The example above is probably not a real world example, but it illustrates the point. The issue could become a bigger with larger guilds of 120 mil with only half active, facing a guild at 60 mil who might not even have players at level 80 yet.