You don't even need to find examples outside of America.
The Amish have also been in America longer than Italians as a prominent immigrant group.
They haven't "integrated" as a function of time in the sense that's being discussed here.
All such historical comparisons are just cherry picking, or finding historical comparisons that fit the author's biases.
One could also claim that Sweden will eventually end up splitting apart along religious lines, as happened in the Indian subcontinent with India and Pakistan.