Interesting! And thank you for the links to your other BDD and Gherkin-related writing.

FWIW, I disagree that a Gherkin requirement should be 5 lines or less and that it should contain only one scenario.

I think that including scenarios other than the successful or "happy" path is one of the primary strengths and advantages of Gherkin. In your example, this might be login failure due to 1) invalid user name and/or password, 2) internal server error, or 3) system timeout.

I've written about all this, including an example template, on my own technology services website here: https://cygnustechnologyservices.com/services/services-more-effective-user-stories/

And at greater length, here on Medium: https://medium.com/@frickingruvin/the-greatest-user-story-ever-told-f72643919ade

I'm eager to read more of what you're written to see if there are things I can learn or improve. Thanks again!