The claims is this article are a little stretched. While the numbers may be lower due to the influence of liberalism and while many things have changed, there is historic continuity among Catholic Christians in America. Catholics who still attend Mass and who are orthodox have maintained a Christian culture in North America. Albeit, a small remnant.
Unlike many "main line" Protestant denominations, the Catholic Church has continued to grow in the US. And conservative, tradition-oriented parishes are doing better than the parishes that embraced the 1960's and 70s psychobabble.