The Kiev mistake cost the Soviets an entire fronts worth of soldiers, took some of their most industrialized areas for weapons production, and opened up a new avenue of supply and attack for Typhoon. How "stupid" and "useless" is it to clear your gigantically extended flanks before going on a huge advance away from your railheads, and setting your enemy up for encirclement (Vyazma-Bryansk pockets)? Contrary to all the German revisionists, the Kiev encirclement was the best thing that could've been done before Typhoon (not to mention encouraging the Soviets into trying to relieve pressure on Kiev, which was a near success but that's another story entirely). When Typhoon was prepared, it was able to be supplied for longer because the supplies caught up and they hit surprised soviet defenders who didn't expect to see an offensive so late in the year.
The victory at Kiev was of course important, but the question remains whether the diverted panzer army contributed to its fall. If I recall the sources I've read correctly then the panzer army wasn't needed.
The real problem was rather the unsolved northern flank which lead Hitler to halt the Moscow advance. He should have used the panzer army though to take out Leningrad.
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