Polish Prussia, Kashubians, Masurians, and Saxonians?

I aware that Polish Prussia is basically land of immigrants, and few times population structure was changed, not just by newcomers from Belarusia, but from Southern Poland AFAIK. More than anywhere else that is situation with population of corridor which was changing hands few times. But what is case with territories which allays were part of Poland. Weren't there complete change of population structure took a place? Isn't autochthonousness of Kashubians and Masurians just myth? What with assimilation of Prussians and possibly of part of Saxonians in Polish nation? Is there any scholarly work about it?

At first I was wondering if this topic was about if it was right for the Teutonic knights to annihilate ancient Slavic and pagan Prussians. But you just want talking about the Germanic remnant with Teutonic origins so whatever.

Well, considering that the German Prussians did annihilated to the Old Baltic Prussians centuries before...even though guilt carrying over generations is some dumb Old testament sh!t and the Russians ruined the once beautiful Konigsburg, there is some cosmic karma aspect to the whole thing.

Anyone?