Yeah I recognize that is an issue with the old system The larger the guild, the higher the (decay/rewown needed for next level) ratio gets and thus for periods where people play less like Mabar - large guilds suffer more relative to small guilds. For our small guild we are about 300k over the minimum thanks to some extra effort from guildies last week. If we earn no renown at all during Mabar we still don't lose a level. However, a larger guild that generated no renown for 3 weeks would potentially lose 3-4 levels depending on the size and guild level, possibly more if the guild was very high level.
A 10% boost for a week for a guild that is treading water won't even cover the renown the lost in one day during Mabar for a large guild.