> Tell me, where does my Jewish German heritage fit in to Germany as an ethnicity? For some reason they didn’t feel very German when they left despite meeting all the qualifications…

That's a good point, and personally one of the reasons I disagree with the ethnic definition of "nation".

The other reason are of course the frisian, danish, sorbian, etc and many other similar minorities that have historically lived in the region of modern Germany.

I think the french definition (which defines the nation almost entirely around the language, not ethnicity or origin) is a much more interesting and useful one. Language determines who you can talk to, and what media you can read or watch.