Would it make sense to support required arguments? For example:

const args = arg({
	'--help':    Boolean,
	'--port':    arg.req(Number),
	'--name':    String,
	'--tag':     arg.req([String]),
});

Alternatively:

const args = arg({
	'--help': Boolean,
	'--path': String,
});

const {
	'--help': printHelp = false,
	'--path': thePath = arg.required('--path', String),
} = args;

arg.required() would print an error message and exit Node.js. Downsides of this approach: Doesn’t handle aliases, redundancy.

If this is out of scope, it would be a good FAQ, because many shell argument parsing libraries support this feature.