From: Southern California
Urban fighting is rather poorly modeled, but even if that got improved, Leningrad would still be extremely difficult to hold. It's the crossing of the Neva and seizure of the isthmus port that kills it. (Or, alternately, taking the Ladoga ports, but that is easier to stop imo.) The city then starves and no real fighting is done for it, it's just a mop up operation.
It is basically impossible to prevent a major river crossing in a light forest hex, even if well fortified, in 1941 if the Axis deploy all his assets correctly. As soon as the Soviet fails a reserve roll, it's game over Leningrad. You'd have to put swamp or heavy forest there to make it really defensible.
WitE Alpha Tester