@Raymond:
"Downstream processing or transformation of inputs is beyond the scope of argparse which should stick to its core responsibilities of argument extraction."

You somehow contradict the official documentation:
"One particularly effective way of handling sub-commands is to combine the use of the add_subparsers() method with calls to set_defaults() so that each subparser knows which Python function it should execute."

The official documentation seems to recommend to pass real Python functions to the parser. So it does do simple "processing or transformation of inputs" which you recommend against.