I think taking it to the realm of New Age or spirituality is indeed going to a certain extreme. There are many cases that do not constitute belief, may still not meet historical research standards as such, but are still worth exploring. For example, there have been any number of threads that postulated something like (not quoting any specific thread here) "the Empress is Venus, Venus is Isis, Isis is Ashtoreth, hence Tarot must be of prehistoric origin." This example isn't that far-fetched, because if one assumes as a given the universality of the images, one could explore the archetypes that constitute them to no end. Ashtoreth is the Empress, the basic symbol of the primeval Mother. Thetis, Artemis, Hera, Athena, Gaia, Binah, Virgo, Shechinah, etc., cannot all those be explored as mythical influences, as different names for a similar idea? Or must I show that Visconti uttered the word Hera during umpty-dumbty-fifty-four, hence we have the Empress? I'm not talking about divinatory interpretation but direct cultural significance.
Asserting that such a connection means Tarot as we know it, the complete assembled volume of images, dates from prehistory is going too far, but the history of myth can still be explored even without direct references. One must tread lightly, however, and not stray into the territory of those that would say semantic connections reveal causality, as in "the fact that there is a rainbow in the sky proves the story of Noah's Ark."
History needn't be a list of printers, dates and dry references only, just as one doesn't need a stone bas-relief of half-Mary/half-Isis to infer that one came from the other. Perhaps the issue is not with the subject matter, but with the way it is presented.