@Beorna
You refer more than once here and in other threads to fact that Slavic of ninth century or tenth century was a young language and so far I have read nobody contradict that point of view with evidence.
Oh, it contradicts, because the thesis which is shown by domen is those of autochthonous Slavs in recent Poland. The "evidence" he presents shalll directly support this. The autochthonous Slavs were more than once used for political interests.
I just fail to see what you are objecting to in Domen's thesis. Domen has presented the physical evidence for idea that population replacement from the East is unlikely. Among many other sentences in your reply you seem to acknowledge the anthropology evidence he provided.
I question the accuracy of these research, the anthropological more than the genetic. I wrote above why. The difference between me and domen is, that he sees the population there as the direct forefathers of the Slavs and maybe as proto-Slavs. Genetically may this be, but these forefathers were neither Slavs nor proto-Slavs, they were germanics or celts or venetics or balts.
If I may as a total layman ask a direct question to you, do you expect that a culture with very limited trade contact to classical civilizations of Rome, Dacia or Persia to have a language as complex and with comparable number of nouns and verb as the languages of other "barbarian" cultures that were in direct contact with the classical civilizations?
I am no linguist, but the german language is full of words, for which in Latin exists only one expression. So I am not sure if high culture means more complex language. WE need our mate midas here.
Would you expect such a culture to be speaking something nearer to the neolithic P.I.E. (proto IE) spoken language?
Every poulation has a neighbour population or more. The Slavic language changed e.g. to a satem-language by indo-iranian influence. If we look at the corded ware culture, we should expect, that the indo-european populations inside these culture had still close relations. And this is supported by linguistic, which places Germanic, Slavic and baltic into a common branch. The difference is, that the western germanic did not participate in the satem shift. So to answer your question, archaizisms may have different reasons.