> Even taking Moscow wouldn't have helped.
I don't think that's widely accepted. There's a reasonable argument that Moscow formed such a communication and transport hub that losing it would have been a significant blow. If Moscow fell it seems likely Russia would have been cut off completely from the West and had to rely on Western aid over the Pacific to the East and then via undeveloped transport networks to new industrial bases. Unclear if this would have worked.
Also worth noting that the loss of Moscow would have meant the loss of the manpower that was there defending it.
I don't mean it wouldn't have been a huge loss. I mean that in a war of total extermination, the stakes are different. Remember that surrender wasn't an option. And in any case, Nazi Germany played their hands pretty badly with Moscow, too.
Nazi Germany sealed its fate with Barbarossa. And it made it even worse by making it a war of extermination (unlike in other theaters of the war), a fight so barbaric and racially charged it forced a desperate defense on the Soviets, because surrender truly wasn't possible; and for the same reason, they ensured the revenge would be terrible.