As far as AG South is concerned, Halder was smoking crack. With only one Panzergruppe [Von Kleist’s], Rundstedt lacked Bock’s ability for encirclements on a large scale. Additionally, he was constrained by geography to a much greater degree than Bock. The Dnieper ran generally east to west on his left flank for a good distance. To the south was the Black Sea and Sea of Azov.Hence, no great turning movements.
He had to deal with a land bridge on his southern flank in Russian hands,the Crimea, which was reinforcible by the Russians until taken by the Germans. That tied up one of his armies [the 17th]. So basically, aside from his Romanian contingents, his striking power was basically Kleist and Reichenau. But Halder is still focused on Moscow.