Funny you should mention Neoplatonism as an example of pseudomorphism. Just yesterday I was watching an episode of the Esoterica channel on Theurgy, and the host made exactly that point about Iamblichus (without mentioning Spengler etc. so quite independently), that Iamblichus, a Syrian by the way, is thought, and thought of himself, as being "purely" Platonic, but actually he discards a number of key beliefs of Plato and even Plotinus and Porphyry, his teacher; principally, rather than denigrating the body and demanding a purely intellectual approach, "theurgy" uses rituals, asceticism etc. to influence the gods and thus ascend back to the One. He emphasizes at the end that Iamblichus' model, which was taken over by the Platonic Academy itself, and even used by Julian in his attempt to re-start paganism, is much more like Orthodox Christianity than our idea of what "paganism" or "classical thought" is. Is this continuity an example of pseudomorphism?

https://www.youtube.com/watch?v=ePhCyVJEAxk