You know how if you hit rock bottom, the only way is up right? Well the inverse can be true too ofc.
Oda hit the absolute peak of the story and characterisation with Marineford and Whitebeard . It fits that the story and Whitebeard's charcterisation become an Icarian tragedy after that, its only downhill from here. So many characters have experience flanderisation and OOC assassination over the post TS too, it's frustrating as hell.
(I do enjoy a lot of post TS, I'm just being somewhat facetious too.)