While as I stated, I can understand your feelings toward my suggestions it has to be admitted that the conventional allegorical model is rather vague whereas mine covers the description far more accurately. However, whether it actually did apply is matter of conjecture as in fact is the generally accepted conventional model.
Platos model is entirely accurate and complete within it's own parameters, but as far as commonality with cosmologies of other cultures there are any numbrer of factors to consider, not least of which is that they all observe the same objective phenomena and attempt explanation from a human perspective, ie the question would always arise as to why heavenly bodies don't fall from the sky, with the easiest explanation being they are supported in some manner.
Having said that there is derivation of aspects of Greek cosmology from the Near East, notably Babylon,and whilst there is also at early dates commonality across the extensive Eurasian territories as far as Northern India, there is nothing to suggest Plato sourced directly from India.
Neither of us can actually prove our case and I am merely giving a further possibility based upon what he almost certainly would have known. I view my suggestions as being very strong possibilities as they take on board so much of his description but I cannot prove my arguments any more than the more conventional case can be proven. Both remain possibilities
THat would leave Plato scratching his head, he has outlined the mathamatical formulation of sevenfold division of a whole into concentric circles, he has in line with other philosophers of his time suggested this as the model of the Universal Soul/cosmos, and the inner workings of it such as musical harmonies, and detailed an idealized city founded upon these principles, he wasn't attempting to create a mystery but provide a solution...
Hence we keep an open mind and keep searching for explanations.
There is no need to look for possible explanations of the theoretical model beyond the given factors he was concerned with, but as far as the rumours he based his tales upon, of a continent before the Pillars of Hercules in the extreme West that's as may be, regarding ancient knowledge of such.