So we’ll start with a short summary of what I understand of the battle of Berlin. The Germans were low on resources and man power, they had a few divisions of veteran units and tanks but they did heavily rely on civilians to include children as a last minute defensive measure, they had little to no air power. That being said the defense barley lasted two weeks where as the soviet defense of Stalingrad lasted longer. Not to mention in Stalingrad to get the Soviets supplies they had to cross the Volga river. Germans had plenty of time to prepare the city and had some what superior fire power like AT guns and tanks (I understand most had mechanical problems but in a static position they should do fairly well) along with fighting building to building street to street.
Apologies if this isn’t sourced enough as I am home for the holidays and away from my resources. The Wehrmacht of 1942 and 45 were vastly different beasts, the soviets also managed to totally cut-off Berlin from reinforcements and supplies before assaulting the city. In the case of Stalingrad the Wehrmacht was unable to totally surround and cut off the city which allowed the soviets to keep bringing fresh troops into the city. Finally by the time Berlin fell, Allied forces were closing in on all sides and German collapse was imminent. Flashback to Stalingrad, and the soviets still held their capitol and the majority of their heavy industry.