One could say the same of most candidates for Greek and Mayan leadership. Yet, they still are widely recognized as Greek and Mayan leaders, because in their time they were among the leaders of those people.
Which certainly can be said of Maria Theresa, a German-speaking ruler of German culture who ruled over a wide number of German realms (plus a few non-German ones), who was (technically by marriage, but it was well understood that she was the de facto ruler) Empress of the Holy Roman Empire.
In every imaginable way Maria Theresa has a *greater* claim than Frederick the Great to being a German leader. The only reason it's viewed otherwise because of people clinging to the ridiculous notion that Germany only really existed from 1871 and that the closest thing to a pre-1871 German is Prussia, since they were the ones who won the race to (re)unify Germany.
Adding an extra civilization for a german-speaking, german-cultured country that was not only wholly part of Germany up until the late nineteenth century, but in fact the *heart* of Germany for most of the previous five hundred years, just because another country won the reunification race is making even Canada and Australia look like reasonable use of tags.