The Germans are guilty to these problems as consequence of colonizing large chunks of Slavic lands in middle ages and onwards. That is the standard Polish point of view I think.
Yes, but if one goes that distantly in the past, it shouldn't be forgotten that most of these lands were inhabited by Germanic tribes before the Slavs arrived. Of course,
then it should be remembered that those lands were inhabited by other Indo-Europeans (Celts, Balts and/or Slavs, depending on which theory you accept) before the Germanic tribes arrived. And
before the Indo-Europeans arrived, there were other inhabitants whose name we don't even know.
So perhaps it's better not to rely on historical rights in these kinds of arguments. Or some of the non Indo-Europeans in Europe might someday claim Poland with the same arguments