The Germans practically lost the war as early as winter 1941 near Moscow. Their blizcrieg failed and they weren’t geared for the protracted war of attrition which was to follow with certainty. Even the Nazis realized it.
Their only hope at that time was a pipe dream of separate peace with Western allies. In 1942 with own resources depleted Stalin tried some poorly planned offensives which failed giving the Germans another hope but it was stupid and actually over as proved in Stalingrad.
Kurks wasn’t really that important being just a confirmation of fact that the Germans are over in the East.
Land-lease was important but it was in fact less than one tenth of materiel used by the Soviets. It was sensitive in terms of motor vehicles and radio equipment. As mentioned by previous posters the Germans were moving of foot and the Soviets on trucks which was somehow sensitive. Was it crucial? Probably not.
Now the allied bombing of the German infrastructure was helpful and also distracted Luftwaffe allowing Soviets to gain air superiority over Germans earlier.
As for the landing in Normandy it is questionable would it affect anything or not in any meaningful sense.
I think the point of the allied land invasion was more to insure that the Soviet forces won’t move beyond agreed zones into Western Europe.
That’s pretty much it.