In the early days we certainly didn't think it through in terms of cultural compatibility, no. Enoch Powell copped on, but picked the wrong target.
Weirder, though, is the idea that Merkel let all the migrants in because of low German birthrates, etc, etc. There are literally millions of unemployed young men and women in Italy, Spain and Greece. Why not encourage them in instead of hordes of uneducated muslim men? Surely if the EU means anything, that should have been the obvious answer, shouldn't it? Does rather suggest it might have been more about German guilt and virtue signalling pure demographics.