Coral Island for summer
Azria for winter (christmas)
Dark Traseia for halloween
Traseia for spring
This could be the opportunity to try and make new things for the events.
And instead of constantly having event mob spawns throughout madrigal, just make the event mobs regular spawns in a copy of these premium areas, replacing the regular mobs.
That way, if people want to farm event mobs, they can do so in a satisfying way without competing against each other, just as if they were leveling.
And it would also allow for some week-end event to make use of event mob spawning throughout madrigal without hindering on the current event spawns (cute invasion, for example 👀)