D-Day: Has Russia's role in ending WWII been downplayed?

The allied invasion of Normandy on the 6th of June 1944 was seen as the turning point of World War II. Commemorations marking D-Day took place in New Zealand yesterday and have been underway in the UK today. But This year Russia's presdientm Vladimir Putin was not invited to join other world leaders marking the 75th anniversary. This comes as Russia has claimed that the significance of D-Day has been exaggerated and downplays the key roles played by the Red army at Stalingrad and Kursk. The head of Defence Studies at Massey University Professor, Rouben Azizian discusses whether Russia might have a point.