Personally I think D-day isnt that big at all, in respect to ww2... It happened in 1944 less than a year before the war ended.
Everyone knew including Germans that the war was over after 1943 defeat in Stalingrad... Without D-Day soviets would`ve won anyway without allied landing. Maybe it would've taken them extra year, maybe less since Nazi war machine was completely obliterated by 1944.
What D-day did was to stop soviets capturing all regions down to Spain, thats what it did.. Pretty much trolled Soviet Union.
Battle of Kursk/Stalingrad even winter war make look D-day like a piece of crap
I mean in both wars Germans sent I think nearly 90% of their armed forces into Eastern Front, I dont think the 10% that the allied took out would`ve had any impact at all on the Soviets winning the war, since by the time russians got to berlin they outnumbered germans I think it was 1 to 10 in manpower/tanks/artilery ect ect... Soviets in 1 night during siege of Berlin launched more shells on Berlin than all allied bombings put together...