Nope, the Germanics were there before you!
Really? Then what great cities have you built there? Poznań, Gdańsk, Szczecin
all the major urban centres in the region have been built by Poles unless of course we include farming communities by the Germanic tribes as a claim virtually all civilized infrastructure we established?
The amusing bit about German premonitions about civilization is that we ddint kick out German tribes, we didnt take over the existing settlements, the places we mention are scratch built by Poles, we literally brought civilization and urbanisation to all lands we inhabit and you claim as yours (with the exlusion of Wrocław, that was the Czech domain).
The "German cities" you mention are all built by Poles and for the majority of their existence inhabited by Poles, but yeah i agree before we came and built cities, castles, roads and churches there were Germanic hunters-gatherers and some villages there, question is that does justify said eastern expansion if everything of note was built by us Poles.