I’m not sure that the problem you propose is very large. If a strong player is in a guild with people lower than them (enough that their presence has a large impact on the guild) then they are likely there because they have friends in that guild, and will probably stay. I think the goal of guilds was always to have players at a similar level working together, so I don’t think this should hurt less powerful guilds, especially because those weaker members probably won’t have the other requirements anyway.