I am not sure that is the way to read that article.
Religious "affiliation" is one thing - it relates to which religion people claim to be from. And while it supports your description, it should be read in conjunction with the " service attendance" figures (with the bar already set low at once a month or more). You can see that nowadays, Ontario, the Maritimes and the prairies are all basically at same "one-person-in-three" level of attendance, while B.C. is somewhat lower and Quebec, at one-person-in-six level of attendance, is blowing every one else out of the water.