As a German I shed a tear of joy for seeing proper Roggenbrot in a manga!
The idea that a German baker would be impressed be the flavorless sawdust pressed into vague bread shapes over freshly baked(!) real bread defies any reasonable belief. It's like suggestion to an Italian that frozen pizza is just as good, or to a French that processed cheese is perfectly acceptable, or to an American that ... well, forget Americans, they are hopeless, but otherwise!
A MODERN German baker, yes. But a baker from the late middle ages? They would absolutely be amazed about the flavors and taste. While the diet of peasants in the middle ages could be quite varied and good (really depended on era and region) it was not even coming close to what choices we have today.