One way to disprove soft-polytheism, monism and syncretic perennialism is to point to the Æsir-Vanir War
Part 3
Common among syncretists and pie perennialists alike share the idea posited by this post. In short, different ethnic faiths have wars amongst the Gods, therefore they are the same conflict told differently either by the Gods or corrupted by men over time and location. Or in the linked post, "Myths of wars between gods exist in other Indo-European religions, such as the Titanomachy of Greek paganism ... It is not at all unique to Germanic paganism."
Let's put this to the test and compare the Olympian Titanomachy and the Æsir-Vanir War.
T: the titan Kronos ate the Olympians except for Zeus who made Kronos vomit his siblings out, leading a rebellion & punished the Titans, Kronos being cast into Tartarus.
Æ: The Æsir and Vanir fight over territory and supremacy, but ultimately lead to a stalemate and subsequent truce.
Do these two even remotely sound the same? No. Oversimplification isn't theology.