As you must have a point from experience, what most of us are saying are from experience as well, and most importantly, experience on THIS server. And we shall continue to talk about American WoE.
History lesson. We only had one castle before. The competition for it was fierce. Ever more so when the new castle drops were implemented. Groups of friends and the strongest people in the server banded together so that they could control it better and hopefully raise the commerce. At one point they were unstoppable. But a group of stragglers banded together too and beat them.
If the server just opened up another castle at that time, no one would go against that certain guild, and either smaller guilds would go for the other one, or just band together and raise commerce themselves. What will happen? No more competition. People would sit pretty in their castles and reap their rewards, without the fun, without competition.
Just so happened we opened another castle. But the population at that time was getting bigger, hence the right move. 2 prominent guilds, but still being attacked by other smaller guilds to the point that even the 2 big guilds that held the castles fought for each other. Still, good competition among players.
And another one opened. But the players weren't enough. Now two big guilds held two different castles, no one could break them, because one, these guilds didn't bother sending an attack party to the other big guild, they'll just grab the castle all the small guilds go after, because it's easy, and there's no defense, and two, as I said, the smaller guilds would just go after the other, least defended castle. This is a move we cannot undo, and still feel the effects right now. A big alliance holding one castle, and two "worthless till the last minute" castles, because not enough players are banding up together. How is 3-5 big guilds controlling WoE, as you say?
In reality there are 2 guilds controlling ONE castle, and a bunch of other smaller/less experienced/less geared guilds having their chance at the two other castles. And this is already boring. What can you call "competition?" People ignoring a certain castle and just trying their LUCK with the "free" castles is not competition. So in saying, if you can't even see the fact that 3 is already too much and it's killing competition, what would more castles opening do? Do not always compare the server to other servers, because however it may still be Ragnarok Online, certain elements could have been adapted to change some things, like, say, the coupon economy. And the incentive to WoE that the rewards are very nice, and with 3 castles open, lots of opportunities to get one. Provided you are PREPARED.
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For Euro WoE, I am still unsure of the move we have to take. Repherion is tight, but the amount of players online is good now at the time. Maybe, there is a need for a new castle, or relocate the Euro WoE castle to a bigger one, so at least one guild can try to set up a defense with more time for setting up after an E-call.