In 1939 there were 111 million people in today's Russian territory, in 1946 - only 97. So literally, yes, every 7th Russian was killed fighting nazis.
By the end of 1939, there was no such state - Poland. There was the Polish nation, but there was no Polish state that exercises its power within its borders. There were Soviet Union and Germany and border between them. And after the end of WWII, Poland was restored. Not just restored, but got about 20% of its current territory from Germany. Only Red army from all the Allies was present and won the battles on this territory. Would you restore a neighbour state and gift it yesterday's German territory filled with the blood of only your soldiers if you just want to conquer it?
By the end of 1939, there was no such state - Poland. There was the Polish nation, but there was no Polish state that exercises its power within its borders. There were Soviet Union and Germany and border between them. And after the end of WWII, Poland was restored. Not just restored, but got about 20% of its current territory from Germany. Only Red army from all the Allies was present and won the battles on this territory. Would you restore a neighbour state and gift it yesterday's German territory filled with the blood of only your soldiers if you just want to conquer it?