There were all kinds of complications. For example they had limited boats to ferry people to safety. These boats operated night and day under mortar and artillery fire as well as air attacks. Later on under direct fire when the Germans took parts of the Volga beachhead. Then when it got colder chunks of ice floating in the current made the waters even more treacherous to navigate.

I'd argue that it was exactly the centralized planning that enabled the Red Army to muster the forces necessary to counterattack and encircle the Germans in such depth that they couldn't break out or be rescued by an outside force.

The idea that keeping civilians in the city would probably make the Soviet soldiers fight harder probably lead to a lot of preventable deaths but that order has nothing to do with central planning.