If OP battles are made GvG only, I don't think that a single big guild could keep as far as 6 OP.
Let's say a big kami guild owns 6 OP. Then 6 karavan smaller guilds could make an agreement and attack the 6 OPs at the same time. So the big kami guild will be alone to face 6 other guilds fighting at the same time in different places.
So it won't be possible for one guild to keep many OPs at the same time.
The only problem to solve is guild hopping.
Let's say a big kami guild owns 6 OP. Then 6 karavan smaller guilds could make an agreement and attack the 6 OPs at the same time. So the big kami guild will be alone to face 6 other guilds fighting at the same time in different places.
So it won't be possible for one guild to keep many OPs at the same time.
The only problem to solve is guild hopping.
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Kaléan McFertyPirate of the Lakes