The native ‘aryan’ population is weak and neutered. Toughness is no longer in their DNA. They can’t build a strong military force with effete snowflakes in skinny jeans.
So they have to import this toughness from some place else.
I think you’d find a miraculous improvement in the quality of their domestic product if the tidal wave of ‘migrants’ were suddenly cut off for a sufficient period of time. Much like a housewife who goes from the world’s worst cook to amazingly competent when the family budget no longer allows for take-out food. As things are there is no incentive for self-improvement because the workers know they’re so easily underbid and a ‘revolving door’ is easier for employers.
Before corporations could hire tens of thousands of slaves in Red China or starving peasants in India or the Philippines they somehow managed to find plenty of competent labor in America. I’m fairly certain the same would happen to Germany, but they’re going to have to shut off the spigot of something that is as addictive to a nation as heroin is to an individual.