I think Bunch is using the "black and white" gambit as a cover for the fact that he is really falling in line with the "warning shot" lingo that Eddie Muller (name-checked here) has been using for awhile about noir in general, but that is now (rather shamelessly) being applied to NIGHTMARE ALLEY as if it is the second coming of FORCE OF EVIL or something. The Icarus myth is cautionary for individuals, not for society as a whole; it's a particular kind of shrewdly addled logic to suggest that Stan Carlisle is an avatar of the Age of Trump, but that's probably the best shot del Toro, Scorsese and others falling in formation with that argument can make to get more folks to watch the film.
As for why it got a Best Picture nod and nothing other than techy nods, two thoughts. One, I'd guess that this is tactical for the Oscar nominators, particularly in response to Scorsese's intervention: as one in ten, it has little chance to actually win (though THAT would be a hoot). Thus it's the safest place they can throw the film a bone, and by doing so they can make the case that they're not really impressed with the "full package" even though they acknowledge that many liked the wrapping paper. And that explains: no actor noms, no director nom, no screenwriting nom.
Two, it has nothing to do with the B&W version, a perusal of which will demonstrate to seasoned noir aficionados that del Toro's claims of simultaneously creating a perfectly compatible greyscale for "expressionist cinema" fall almost laughably short of the mark. So much of the lower foreground of the film is encased in deep, dark grey mud that despite the crispness of the imagery in the other quadrants of the frame you are sometimes wondering if you're looking at a second or third generation copy of the original. There are some striking moments--the much-circulated photo of Cate Blanchett lighting a cigarette from a match seemingly "borrowed" from those filmed and lit in DOUBLE INDEMNITY--but so much of the time Bradley Cooper's face is overly shadowed that it's clear that del Toro and his DP Dan Laussen don't really get the technical aspects of what classic noir lighting is about.
Compare the B&W version of NA to Joel Coen's TRAGEDY OF MACBETH, which probably lost out on a Best Picture nom due to the back-room machinations with slot #10, and you'll see the difference in how to use B&W. We can hope that Bruno Delbonnel, DP for MACBETH, will bring home an Oscar for a film that wound up under its pay grade, with only three nominations (best cinematography, best production design, and best actor for Denzel Washington). FWIW, Variety gives DUNE the best chance for the cinematography award, with MACBETH #2.