Anders,
the problem is the strong US/EN-centric way the projects are handled by WMF. That drives people away (especially the more critical/touchy communities like DE), and it didn't start with the superprotect mess. There were other serious affronts by WMF (image filter, etc.) to the community before that, but don't let us delve into that now, everyone following this list in the last 5 or so years knows what is meant. ;)
Moreover, how is this "impact" measured? By number of uploads/new articles etc.? The dewp community has always valued quality much much higher than quantity. Does WMF even have a decent way of measuring quality for that impact assessment? So before looking at WMDE's performance to keep the community alive, one should first look at WMF's and there I see many shortfalls as well. Nobody can link the editor decline in DE projects to WMDE's performance alone. There are just too many other factors, including cultural differences, that need to be taken into account as well.
Th.