In general, that is true. Although I would include other larger cities along with Paris. But most Frenchmen did find it a bit odd. But that was then. Today, France is a VERY secular nation. And the USA is so multi-religious the Gregorian calendar here is absurd, as it is in Israel, China, and Saudi Arabia. Better to use an entirely secular one for secular purposes, and leave the religious ones for that. But, hey, it's cool. Just my thoughts.
Also France still hold a large Catholic population. And regrettably also a lot of newcomers.