People are watching this season with the wrong expectation. This season is not about ending the whole story, it's simply the end of the conflict with Marco. The bits of history we see from Laconia are just an introduction to something that will be worked on later. So the last ep isn't going to solve everything, it's just going to solve the war with Marco and leave loose ends for the future. This is just the end of the "second trilogy" of the series.
The "last trilogy" (last three books), we'll have to wait and hope to be adapted.
The "last trilogy" (last three books), we'll have to wait and hope to be adapted.