I would love for you to expand on this, and name names… Using your own terminology, I would put “vermouth di Torino” and “Marseilles and chambery dry” in the “classic mixing” category, and with “western dry” and “modern” firmly in the “standalone” category, and Spanish, chinato, and alla vaniglia arrayed in the middle…
Ok.
I would put essentially everything that has been cast as “western dry” in the not-actually-vermouth category and bid it adieu with the proviso that it’s welcome back once they stop calling it vermouth. However, most of those weren’t really good enough in the first place to stand on their own merits. I long ago stopped buying and trying every random “vermouth” that hits the shelves, but several from Ms. Lamb’s haul probably qualify as not-actually-vermouth. Instead of playing whack-a-mole and antagonizing lots of people, I have found that if I wait a little while, these products inevitably fade out on their own.
The “Modern” category—as I have used it in the past—was a bucket for various comparatively-recent vermouths that did not fit into the red/white/dry mainstreams established by ~1910. They are all edge cases produced from within the regional traditions by producers who know what they’re doing. Every one of them gets mixed with (to the limited extent they get used at all), but they aren’t really drop-in substitutes—they generally demand a drink be constructed around them or they drag a familiar template into a distinct new identity (a new drink). Also, that these “modern” vermouths tend to not be home runs—they are perhaps interesting and enjoyable, but most people wouldn’t buy a bottle twice.
Is there any real vermouth that isn’t mixable? Not really. Is there any real vermouth that isn’t drinkable on its own? Yes. The entire dry vermouth category is essentially mixing-only (although the new Cocchi is almost a gotcha). There are plenty of mediocre vermouths I’d probably take a pass on sipping, but I don’t really want to mix with mediocre vermouth, either.
As for the health of the vermouth (and its relatives) market in the USA, here is the back bar of a very popular bar in Greenpoint, Brooklyn:
While it’s difficult to spot customers, even in the mirror, this bar was packed inside and out, and I just managed to snap the photo when both beleaguered bartenders were rummaging around off camera left.
Everyone at this bar is drinking vermouthy stuff in one form or other. Nobody is drinking it completely straight, but one of the popular house specials comes fairly close:
This is vermouth—from a tap—over ice, topped with orange foam. A bit sweet, but doesn’t suck. And as soon as one person orders it, everyone else does too.)

