....much less the commander of an army in the field
Agree totally with everything you said, Mike, except this snippet -- although I do mostly agree. In a fight, there were few better than John Bell at maneuvering into and directing it.
However, you did say "army," and here is where I agree. He was totally unsuited for all those things required of army commanders. For example, it would appear that at Spring Hill, Schofield was let pass because his commanders did not (did not dare?) throw troops across the road -- a SNAFU of major consequences. Would any other commander have gone to bed with such a providential opportunity in his grasp? Would any other commander have subordinates who were afraid (or reluctant?) to act?
Just this one piece of evidence supports your conclusion: he was in way over his head.