Those are intriguing questions. I find it ironic that, despite the long-held (and IMO spurious) notion of the "American palate" preferring sweeter things while the Europeans prefer bitter and dry things, the version of Noilly Prat dry vermouth that was exported strictly for the American market was much drier than what the European market had access to (which we all discovered when they reverted to the "original French dry" formula). The original is arguably sweeter and fuller bodied than the Americanized version we had.
We often speculate about how much "Italian Vermouth" might have changed since it's commercial invention, but people seldom question the nature of French Vermouth.
I often wonder when I come across cocktail recipes that call for a dashes of French Vermouth. It just makes no sense to use modern Dry Vermouth. I might as well add a dash of water.
How have the formulations of French Vermouth producers drifted from what might have been produced at the beginning of the 20th Century?
Were the "French" vermouth formulations of that time closer to what is sold today as blanc/bianco vermouth?
Like most other aperitifs, has "French" vermouth drifted towards drier and lighter?
As for bianco vermouths, M&R's is extremely sweet, so I would be surprised if French vermouth was ever that sweet. Dolin's Blanc isn't as sweet, of course, so maybe that's closer to being possible (and it is French).
Sidenote: I just recently had the pleasure of tasting Dolin's vermouths for the first time, thanks to a kind bartender who graciously offered me samples of all three varieties merely because I said, "Oh, you have Dolin vermouth." There were all wonderful, so now I'm dying to get my hands on some.