The reason grammatic gender is called gender is because almost all nouns referring to men (boy, men, father, uncle…) are in one group and almost all nouns referring to women are in the other.
In German, Mädchen is not in the female group because -chen is a diminutive changing any noun’s group to neuter. The word Jungchen, from “Junge” meaning “(young) boy” exists as well and is also neuter.
Similarily, all plural nouns are in the female group. Just because grammar has some more quirks doesn’t mean grammatical gender doesn’t line up with actual gender.
The only exception in German I know of would be the word “Weib”, cognate to wife, translating to women, which is in the neuter group. Except this word is archaic and an insult nowadays. All other words referring to gendered people should be in their corresponding grammatical group.