Under the old system a guild of 5 would have had decay based on 20. A guild of 200 would have had decay based on 210 so the small guild bonus really only helps small guilds break even in that regard. If 20% of the small guild is online earning 240% they are geneating renown to cover 2.4 out of the 20 used in the decay formula (12%). If 20% of a 200 guild is online they are generating 40 out of 210 used in the decay formula (19%). Under no circumstance does the small guild ever come out ahead with regards to math if the same percentage of guildies are casual, inactive, skipping chests or leaving renown in chests. But there have obviously been some focused guilds (usually around 10-20 people) that have been able to reach very high levels due to high play time and strict recruiting standards. Zerging guilds also get more renown generation because chests are opened in a smaller amount of time.
I do acknowledge full that people in large guilds tend to have more complacency with regards to renown generation. That is a big challenge for large guilds and this should be dealt with so that large casual guilds can advance. But any notion that small guilds can overcome these issues easier than large guilds is completely false. Large guilds will sail to level 50 even with no concern about guild renown. Most small guilds will never get to 50 and many will just disband due to lack of progress. I would like to see people have a choice between small and large guilds - based on their personality and preferences. I also want to see the big guild issues resolved. I have many in-game friends that are in big guilds and I want them to have a chance to get bigger ships and better amenities.
I don't agree that large guilds are out to help casual players while small guilds are not (not directed at you - but I see these type of false comments in this thread). Many people get lost in large guilds and find a better home in small guilds. My small guild never booted a single casual player and we only booted inactives that were gone a long time and obviously not returning. When someone asked to join our guild we never declined, we only asked that they agree to represent our guild well with kind behaviour to others. We don't reject people because they aren't hardcore players.