My take on The Last Temptation of Christ as a Christian is this: From a strictly orthodox perspective (small "o", I'm not talking about denominations here), then yes, it is, technically blasphemous, in that it introduces narrative elements and ideas that are not present in the gospels of Matthew, Mark, Luke, and John.

However (and it's a big however), at no point does The Last Temptation of Christ claim to be based on the gospels. Both the book and the film are fiction, and as such, I think Christians do the film a disservice to look at it through such a narrow lens. Unlike, say, The Da Vinci Code (which introduces as "fact" ideas that are not merely blasphemous but outright heretical, not to mention historically absolute nonsense), The Last Temptation of Christ is not making any claim on being factual. It is a speculation that grapples with attempting to understand how Jesus could have reconciled being simultaneously divine, yet limited within three-dimensional space-time by his human form. It is, as you rightly point out, deeply relatable in that sense, and I believe it is potentially (and sometimes actually) a vehicle for helping believers better come to terms with the more difficult elements of their faith.

I think the film is also an honest reflection of Scorsese's struggles with his own religious beliefs, and reflects where he was at that point in time. I don't think he'd make the same film about Jesus were he to make one today, as he seems to have come back to the Christian faith (specifically Catholicism), and I think this is inherent in quite a few of his later films (The Irishman, for instance).

Great article. :)