Right now, there are guilds with only 6 members that have reached level 90+. This is because they're getting q 300% renown bonus. There are guilds that run just as much as they do, but have more people and are lower level.
My suggestion is to remove Renown Bonus! That's right, everyone gets the same standard renown amount.
BUT larger guilds will gain a higher decay, smaller guilds will have a lower decay.
This would mean all guilds would have a harder time leveling up, but the renown cost per level could easily be cut in half! What would this change do? Smaller guilds would still have an advantage, but they won't get 4,000 Renown from a Legendary Victory.
Larger guilds want an advantage of having more people? They gain more decay. Smaller guilds can't exploit the system by merely being smaller. This way, everyone gets exactly what they work for.