Inconsistencies with the sundering (Spoilers)

[PeaTearGriffin]

You're going at this as if the writers completely ignored or changed world events, which is not true.

You can move the goalposts all you like for the definition of retcon, but like you said already, it's "explaining a new additional reasoning for the Sundering."

A new additional reasoning in the endwalker cutscene that recontextualizes or breaks continuity with how the sundering was described in shadowbringers.