If one defines the metavar different from the argument name, like in:

@adapter_group.command('list')
@click.argument('CPC-NAME', type=str, metavar='CPC')
@click.pass_obj
def adapter_list(cmd_obj, cpc_name):

the usage line in the help text correctly uses the metavar:

Usage: zhmc adapter list [OPTIONS] CPC

but the error message when invoked without arguments incorrectly uses the argument name:

Error: Missing argument "CPC-NAME".

I suggest that the metavar is used consistently in all display to the user.