Landsknecht would have come about in the 1500's. Which is a good thousand years after all of this. As it stands the German states and culture wouldn't even resemble the German state and culture we know today.

Otherwise, the tribe of Germans that sacked Rome in this era would have been either the Visigoths under Alaric, then Vandals under Geiseric, and then the Ostrogoths under Totila.

But there hadn't really been a tribe more dangerous to Rome and its values until the Lombards. But the Lombards are a whole other thing involving the Catholic Church, the House of Karling, and the Holy Roman Empire. And they didn't really even get to Rome.