My comment was simply this:
1. Small guilds get a bonus
2. Small guilds get a second bonus when decay is calculated.
Large guilds do not.
Now, your argument that it is more about activity is correct. YES a HUGE guild with 100% active members that played every day would still achieve faster.
That however, is not reality. In reality with larger guilds you get some members who are very active and others who are casual players. This system punishes u for that. It basically forces u to either purge the weak, or not care. Frankly, I don't think you should punish a group for allowing the casual weekend player to stay a part of it. By setting up the renown system the way they have, Trubine is in fact punishing u for allowing less active players in your guild.
And the numbers support this. Look at the leader boards across servers and you notice that the larger the guild, the less likely they are to be in the top ranges.
I play WoW as well as DDO, and I see the cut throat nature of guilds there and I prefer not to see it here as well. I know it has affected us at CK and how we look at adding new people. That is sad.