The real issue is kind of semipredicate problem, which is avoided in your special example but can't be in general.

So what happens if the first positional argument is a hash ref and not a string like in your case?

How can you tell that this ref doesn't represent a hash of named arguments?

If this happens you'd need to diverge from your interface standard and will confuse yourself and your users.

Better stick with a convention which doesn't need special cases.