So a good way to use renown to nerf big factions is to have renown influence how much population will fight during a raid.
A huge bonus is a big faction has over a small one is manpower. For example my carebear faction can have competent army leaders that dont own fiefs, meaning the fief owners in my faction are always close to home and we can keep gear on them for their fiefs in case a raid goes down on a 0 troop fief. Smaller factions cannot afford do this and keep a strong standing army in field.
what if A fiefs population fought in raids? The number of pop that fights would be equal to 1% of the renown of the your lowest renowned member? We have army leaders with 200k+ renown, yet we have 90+ members with around 7k renown
So small faction could have no problem getting all of their fiefs to get pop in raids, while big factions will never have much at all.
Edit: just realized i used so for every paragraph lol