It largely is, at least when in reference to Napoleon, who technically never waged war in Russian in winter (the last troops left the country on the first day of winter). But even when we do not nitpick and treat 'winter' as a 'cold season' (autumn was exceptionally cold that year), it mattered little in the defeat of the Grand Army, 'only' contributing to the attrition rate, as I wrote in sligthly more detail in this thread.