I've not flown the Stinson "hot n'high", but the movement from fully rich to leaning for cruise is very small, and it *may* be leaned for best power. Or the pilot may have failed to do that necessary thing and can adds something else to his idiocy. In any case you can't actually see the mixture control during any part of the take-off roll, only during taxi, so I think that the case is unproven.
G