This is the last time I will discredit this overall idea
Hitler (Rightly) rejected this idea for the following reasons
1. The donets basin was vital to keeping the nazi war machine fueled with vital materials, abandoning it was tantamount to death for the war effort
2. There was no garuantee the Russians would attack where Manstein wanted them to... 2800 miles of front leaves only a few kill zones, and a lot of room to advance... this is exactly what happened in otl, after kursk, the russians attacked in the far south on the mius, manstein caught them in the flank and destroyed them, however in doing so he uncovered his left flank, and zhukov obliterated him with 3 army groups
3. The days of great sweeps of German armor being effective where over, not only because they couldn't keep air superiority over the battlefield generally, but also because the newer generation of german armored fighing vehicles where no reliable or practical over long distances