This is the sort of story that Endwalker (or rather the expansion that should have been the first part of Endwalker) should have already told, one in which the Eorzean Alliance doesn't march into Garlemald on their own but as part of an international effort that would include representatives of Garlemald's former satellites, some of which would absolutely want to see every last Garlean responsible for upholding the system at a stake.