I like where you are going a lot... GND is given as an example and for any source including the GND we know things can be wrong as well. They regularly are and there is a process in place for indicating where GND and WP-DE differ. This works well because in time the GND does look and remedy or comments. So when a source differs, we need a report. Such a report is GOLD. Because it enables us to verify what is right and what differs. The people who care so much about sources will have a field day with this BECAUSE it is actually worthwhile to spend time on such differences.
When GND has data and Wikidata does not, we should import from sources. I prefer data over no data any day. Particularly when we strive to have comparisons between multiple sources.. Nonsense will weed itself out in this way.
What we need is a process of reconciliation of what is there in the first place, where sources differ and how we deal with eventual changes in the sources (they do include the various Wikipedias, Wikisources, Wikibooks, Wikinews, Wikitravels..)