I suggest recreating the "Garrison" event to be similar to Besiege and Campaign, in that schedule hordes attack "forts". Think of Garrison as low~medium levels campaign. The drops will remain the same and anyone can freely take on the challenge solo or I. Groups. No additional "quests/mission ops" needed, as in Wings of the Goddess.
Much like Besieged, the "Conquest" map will inform player when the target a zone if currently mob hordes are on the "March". I do realize the level of War seen in Wings in not the same as in current day, but I suggest just ignoring that aspect.