I think the campaign was doomed to fail from the moment the Germans entered the city. The Wehrmachts strength was in its mobility at that time, they didn't have Tigers and Panthers, just some MK IVs and the smaller ones and most of the supply train was still done by draft animals. They were over extended and getting bogged down there was the last thing they needed. As their supply lines stretched the Russians supply lines shortened. The Germans had one hell of a time supplying men and material in that type of combat enviornment. This gave them an edge although it was not the only factor.