Its clear that the Russian's poorly handled massed armour but were learning. The Russians were also continually counterattacking. This tied up lots of Germans around Voronezeh.
The German summer offensive of 1942 was spectacularly successful given that it wrote down about 12 armies. However even with that spectacular success, it still wasn't enough.
An important thing to remember is that the German summer 1942 offensive hit the Russians in a sector of secondary significance to them. The Russians deployed their reserves to defend Moscow. When AGC did try an offensive south of Moscow, it got stuffed.