You need integration initiatives and strong enforcement. Integration is a two-party process, if either side doesn't take it seriously, it won't happen. We should be generous in giving out chances, but strict in taking them away from people that prove they're not making use of them.

The last argument is empirically incorrect. Think of Vienna for example, most of the population there has roots from all over the Austrian Empire. Yet, it's distinctly Austrian.

It's not a given, it takes effort. But it can be done.