I think the game is built to force players to join a guild. Players are unable to solo level in many areas due to monsters weaker than them still overwhelming their potions. Bosses and OaDs are designed as well for groups. A player can only solo the game until about level 14 when they begin to have issues depending on where they go to level. By level 17, players can find nearly nothing to do on their own so are forced into guilds to continue playing. Part of this is due to the structure of the game itself but most of it is due to the building philosophy of the areas.
skipping specifics on areas
One easy way to remedy this is to correct the errors where monsters are too strong for their supposed level and areas are altered to provide the correct challenge for solo players instead of forcing groups (i.e. guilds). Build areas, OaDs, and even Mini-bosses that can be tackled by solo players at their appropriate level. Make sure quest rewards are level appropriate as well as fit into the area. Even the implementation of creative events can allow a solo player to shine instead of being dependent upon a guild. All that it takes for this method is for a different approach to building as well as closer oversight of monster/area power as it applies to a single, average player.
If you look at it from my above standpoint, guilds themselves are not the main problem but are a natural reaction to other problems. I've worked on many games over the decades including RoK and many issues are caused by poor planning or comprehension of the underlying problems.
Who knows though. Maybe I'm wrong in my suppositions and observations. I've not gone to Staff yet to discuss my ideas since I've been waiting on the update before jumping back in 100%. Hopefully we can figure out what the underling problems are so we can fix them.