It really is a tale of the Christ, not a Hollywood spoof
I enjoyed the movie's wacky look at Hollywood of the era, but I don't think it was meant to be the focus. Audiences can't be faulted for looking only at and being disappointed by the comic relief, though, as that is how the movie was promoted in the trailers.
After the opening scene, the words "A Tale of the Christ" wipe onto the screen. We are then immediately shown Mannix to make the connection. Mannix shepherds a vast world populated with sinners, but who ultimately create good. He stands over bickering religious leaders, growing frustrated at their interpretations. Mannix considers his worst sin to be smoking, so it's no wonder the Devil, a head-hunter from Lockheed, tempts him with a cigarette as they meet in a very red restaurant. Mannix is offered an easier path, but one that leads to destruction rather than creation. To me, Mannix's struggle with which path to take is the crux of the movie. It is only after seeking his Father's advice that the decision is made.
Other elements of note are the demons (the blacklisted writers) who have stolen away Baird, one of Mannix's flock. Ultimately, the angel Hobie brings Baird back to the fold, while we see one of Mannix's truly lost ones pulled down into Hell (or the Pacific Ocean, as it were). The wayward son Baird is welcomed back, but when he extols the virtues of his captors, he is sternly punished with a regretful slap. Humbled Baird resumes his role in Mannix's creation, though Baird again shows he is not perfect when he forgets "faith."