I think ATS was rushed, because in the Making Of ATS, the timeline for the album started out about February, 7 months before the release. Up until that point, they had been working on a lot of other songs (according to Chester), which were the ones that sounded like PTB and WWDK, which, imho, sound very different in style than the ATS batch.
Fingers still crossed for my original theory that they took the Post-MTM/Pre-ATS batch of songs and refined them into a perfect blend of the three eras of LP ^.^