You do realize that there are plenty of other reasons than guild renown for having a small guild?
Like, maybe, I dunno, wanting a small, organized and active group of people to play with? Or having a guild that only has IRL friends in it like my very first guild.
Thinking that every small guild was just looking to exploit the system is ********. Some of us don't want to randomly just recruit lots of people, guild renown doesn't even enter the equation much of the time. Our guilds are more about small, tightly knit groups rather than having tons of random people with the same guild name.
If this new system is to stay then just remove guild levels completely because they're going to mean nothing at all.