So you and the Austrian authors claim that Albanian is not a descendant of Illyria and is linked to Messapian. Okay. But then where does Albanian come from linguistically, which is the ancient linguistic group it derives from or is most closely related to? Some alternative scenario should be proposed, not just denying the Illyrian links.
I have read a pretty sensible (to me) text about other possibilities for the origin of Albanian, and its basic point is that the very Albanian-like substrate in Romanian, the heavy Latin and more specifically Eastern Proto-Romance and many other linguistic and historical factors could indicate that the ancestor of Albanian was spoken in Moesia or somewhere near it in more lowland areas, in present-day Southern Serbia, in close contact with Romanized people before the Slavic and other migrations pressured people out onto the mountainous areas. But then the question would be what Moesian was like, whether it was Daco-Thracian or Illyrian or maybe a separate buffer branch between them.
I actually doubt very much that the entire Balkans had only four native languages during the Roman Empire: Thracian, Dacian, Illyrian and Greek. We should not trust ancient authors to be linguists or even people very interested in the correct linguistic affiliation of foreigners, particularly those they saw as barbarians. People lump together all ethnicities whose language and culture seem broadly similar even today, to the point they make gross mistakes like calling Turks and Iranians "Arabs". I doubt that was not the case in Antiquity.
So in my opinion one should be a bit careful to dismiss any links with Illyrian or with any of the other main linguistic groups identified by the ancient historiography. Those may have been generic terms to make things simpler, roughly like "the Slavs" even if they speak different Slavic languages.
So in my opinion noticeable differences between Albanian and Illyrian, countered by some apparent cognates, may simply indicate that it was actually a branch of related languages, not one common language. Or it could be, as there are also in my opinion plausible evidences to support this, a Central Balkanic language with unknown affiliations, but possibly related to Thracian or Dacian (but then the links with Messapian in South Italy on the other side of the Adriatic would become a bit more challenging to explain).
