i think guederian was a better commander at corps level rather than field marshall.
also hes a panzer tactician, if he were a field marshall he would be commanding infantry and panzer but mostly infantry which wouldnt suit his "needs".
look at rommel in north africa, he was good at commanding 2 divions but once he had an army he didnt know how to handle it properly.

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News today, a man has fallen into a chocolate vat in the arnotts factory

In other news arnotts have anounced that there will be 50% more tim in your tim tams.
(p.s. only aussies will get this joke)