I live and breathe for articles like this. Thank you.

Please think of the following points as elaborations rather than arguments.

1. The USE of Campbell is a problem, because Campbell is describing certain universal tendencies in myths (the DESCRIPTIVE approach), but he is not writing a guidebook on how to create a myth (the PRESCRIPTIVE approach). Take a screenwriting analyst (let’s call him Vis Chrogler) who analyzes x number of successful films and finds that many (not all) use the pattern of A HERO WITH A HAT RESCUES HIS BELOVED FROM A VILLIAN WITHOUT A HAT. Chrogler then writes a book called The Screenwriter’s Journey: Mythic Structure For Screenwriters, in which he instructs screenwriters in how to lift Campbell’s invariant formula of A HERO WITH A HAT and use it to create appealing scripts.
   There are two problems here: (1) All any screenwriter using Chrogler can do is write a script that sounds like a successful story by, for example, George Lucal (yes, it’s true that Lucas used Campbell, but he didn’t use Chrogler). (2) Studio executives who read Chrogler’s book (and let’s face it they’re not the most creative of Hollywood talent) will tell their readers to look for MAN WITH A HAT stories, and from the slushpile of a zillion crappy, derivative MAN WITH A HAT stories, the gatekeepers will (at best) pick the few scripts that don’t stink totally, and maybe one or two will be filmed, which will confirm the “wisdom” of Chrogler, even though these stories are probably less entertaining as scripts than Porky’s 3. But clever casting and lots of promotion will send these mediocre storylines somewhere near the middle of the morass of mediocre movies.
2. There are many myths besides the so-called Hero’s Journey. Just of the top of my head, the Pandora myth, which has served as the basis for Kiss Me Deadly, Gremlins, and Fallen. If using myths is a powerful tool but writers limit themselves to a small subset of available myths, then the quality of writing will suffer.
3. Many storylines are anti-heroic (you get into this in your analysis). And anti-heroic stories are quite old in moviemaking (Scarface — the original — Public Enemy, The Ladykillers, the Killing….). Interestingly, many of these anti-hero storylines have a collective protagonist, especially heist films.
4. The whole point of the Vis Chrogler / Snake Blyder / Fyd Sields industry is to convince lazy screenwriters that they too can craft a successful ($$$) screenplay if only they adopt the MAN WITH A HAT or whatever formula. Now these lazy screenwriters may have a profound story somewhere in their heads, but they’ll never get it onto paper if they take the short cut, i.e. follow the “color in the shapes” approach of the Paint by Numbers school.