It was handicapping the Polish nation, Dariusz, not exterminating them directly.
The Soviets set out to rid Poland, and the rest of the empire, of a certain class of people.
I think, with all respect to you both, that you have in a sense misconceived Dariusz's point by forgetting the dynamic of the era to which Dariusz speaks of.
Link/source anomaly aside, Dariusz points to the epoch when the Jerries and Soviets were allied, and whose raison d'etre, amongst other things, was the destruction of Poland and its people, and had the alliance survived and manifested its full potential there is grave doubt in my mind that Polish people (inclusive) would have survived past their use as perhaps slave labour and for maybe a few decades.
Obviously, it would be near impossible to objectively prove that the 'extermination' would have taken place, because it didn't, in fact, happen, and one cannot prove a negative, though many try and fail. However, having regard to past similar fact evidence of Soviet (and Nazi) conduct during the period of alliance (and, arguably, post same), lines of enquiry indubitably lead to the point whereby the statement "Poland was not the target of extermination" ought to be replaced with the query "How did Poland survive extermination".
Where there's smoke, there's fire - just because the fire created during the alliance was reduced to smouldering smoke by the Russians post Barbarossa doesn't mean that the embers ever died. The new dynamic of the Big Three alliance also thwarted Stalin in carrying out his agenda re Poland and its people.
A parable would perhaps best illustrate my point:
A tomato was eaten when ripe. Of course I now can't absolutely prove that that tomato would have rotted, because it was eaten prematurely and never had a chance to rot. But, left on the bench, untouched, given time it would have rotted, having regard to what tomatoes do if left to their own devices. Sure, it can be argued that it may have only partially rotted, or it may not have rotted at all, but similar fact evidence regarding other tomatoes rotting would compel even the most ardent sceptic to accpet that tomatoes do, in fact, rot.
Katyn was a part of the full extermination of the Polish nation.
I agree. It was a link in a chain that was severed after the SU and Germany turned on each other.