I have found a source directly comparing US to German middle incomes incase you're interested. Figure 7 of this publication [1] seems to be relevant to this discussion and shows that the median net worth in all groups in Germany is lower. However it compares USD to EUR. Some of the other graphs in the publication showing wealth distribution may also be interesting.

[1] https://www.diw.de/documents/publikationen/73/diw_01.c.53312...

EDIT: The publication isn't the newest, being from 2016.