Well, I think unless the level (not rate) of the two secularisations is synchronised, that's irrelevant, e.g. won't change the status of immigrant secularisation as an indicator of integration. And even if they are synchronised, it is a question whether one is influenced more by developments in the society you left or the one you live in. (Not to mention developments in the local community you live in, ghettoised or not.)

_{*Lunatic*, n.
One whose delusions are out of fashion.}