Same problem, different area...
Like the Atlantic Wall, the Germans can either thinly guard everything, or fortify a few points. Same on the Eastern Front. The Red Army at this point can do a "Bagration" against AGN, AGS, or AGC, almost at the same time. Plus the Russians mastered deception, and I believe Kursk ruined the Heer armoured units. So less defeat would be Germans not attack Kursk, withdraw some, 1943 OTL till Bagration, Germans figure out where it is, and strip the rest of the front to defend there. Problem is, even if Germany inflicts 10-1 dead, Russia can take it. After all, Germany has to defend Italy, France, Hungary, and Poland, and stealing from Peter to pay Paul doesn't work when both are poor...