I suppose the tide had turned against them even earlier, but I highly doubt the SU could have actually made it all the way to Berlin without American aid, even before invoking D-Day. Big mobile successes like Bagration would not have been possible without American Studebakers.
The Soviet contribution was larger no matter how you measure it, but German deaths is not a perfect metric. As early as 1943, the majority of the Luftwaffe and all the Kriegsmarine were deployed against the West. Deaths were comparatively low, but costs of production very high.
