Now in its world premiere before a planned 2023 Broadway opening, “The Devil Wears Prada, The Musical” runs the gamut from mildly diverting to mostly egregiously disappointing, the latter being its defining ethos.

Running through Aug. 21 at the Nederlander Theatre, the Elton John-scored take on the world of high fashion has its work cut out for it. For now, this behind-the-scenes tale set at the world’s pre-eminent fashion magazine is more JCPenney clearance catalog than couture.

“The Devil Wears Prada, the Musical” (book by Kate Wetherhead, lyrics by Shaina Taub) is rooted in Lauren Weisberger’s 2003 roman-a-clef about working at a major fashion magazine, penned after she did a stint as an assistant to Vogue magazine’s infamously exacting chief editor Anna Wintour.

The novel’s dishy scenes of opulence and overwork spawned the 2006 movie version famously starring Meryl Streep as Miranda Priestly, editor-in-chief of Runway magazine, and Anne Hathaway as Andy Sachs, a new hire who believes fashion is frivolous and sees Runway as way to pay the rent until she can change the world writing about social justice issues.

One major problem with director Anna D. Shapiro’s staging of the musical “Prada,” starring Tony Award winner Beth Leavel as Miranda and Taylor Iman Jones as Andy, is its underwhelming sense of fashion. Frankly, you’ll see more creative silhouettes on any given season of “RuPaul’s Drag Race.” Costume designer Arianne Phillips often tries to make sparkle or oversized graphic prints atone for unimpressive design, but much more than a bit of superficial flash is needed. Every look — from an ill-tailored red dress Miranda wears to the office to the bulbous, armless, Michelin-man-worthy creations purporting to be cutting-edge Parisian runway couture — looks under-budgeted and poorly finished.

We never get a sense of Runway magazine, either. We’re told — numerous times, in reverent tones — about the legends and icons who have walked the magazine’s halls. But there’s no sense of detail or history — not so much as a fashion illustration — in Christine Jones or Brett Banakis’ set and media design. The office aesthetic is basic and generic, the fashions within resembling arts-and-crafts projects with little actual art.

More troublesome, “The Devil Wears Prada, The Musical” feels written by committee, some tackling Gen Z issues (there’s a drinking song about “jobs that pay the rent,” and a meaningless jingle about how to live in one’s 20s), some dealing with fashion, some tackling the plight of pioneering women in the workplace. None of these elements coalesce into a compelling story. None is addressed with any particular intensity or ingenuity.

Then there’s the music.

One of the best of the dismal song offerings is a sung/spoken soliloquy-like number from Miranda based on the movie’s iconic speech that uses a cerulean blue belt to explain the global social and economic reach of the fashion industry. In Miranda’s succinct explanation of fashion’s inescapable influence across the globe, Leavel delivers an ice age’s worth of shade, freezing Andy’s scoffing into silence. Even though much of it is spoken rather than sung, it is still the high point of a score that’s otherwise mostly as flat as a newly ironed hem.

The title tune is a head scratcher. Its pulsing insistence that Priestly is actually a devil in designer duds all but undoes all the work Leavel has done to show Miranda as anything more than a one-dimensional, narcissistic elitist. Elton John wrote brilliant scores for “Billy Elliot” and “Aida.” Here, his music doesn’t further the story or deepen the characters. Worse, it doesn’t provide a single, memorable star-turn for the leads.

Jones and Leavel’s adequate performances are bolstered by a supporting cast of characters drawn from the movie and the book. Runway art director Nigel (Javier Munoz) is the quintessential sassy best friend, right down to a withering aversion for synthetics and a predictable number about growing up gay in a small, homophobic town. Miranda’s first assistant Emily (Megan Masako Haley) is all high-strung ambition. Andy’s friends and roommates serve mostly to bring up a brief plot point about housing insecurity, an issue that is solved almost as soon as it’s spoken of.

Under Shapiro’s direction, “The Devil Wears Prada, The Musical” attempts to emulate the movie’s lightly comic, somewhat acerbic exploration of an industry that’s all glamor and wealth on the outside, something much messier on the inside. She succeeds only in creating a faint copy of a copy.

In its current state, “The Devil Wears Prada, The Musical” is a poor knockoff, a cheap flea market bag with a designer label glue-gunned to the lining. Back to the sketchbook!