So, really, it doesn't matter whether it's a divisional opponent or not.
Miami knows us. We know Miami.
Whoever plays the better game will win. Just like opponents from another division or conference.
It's an urban legend as you say.
https://www.google.com/amp/s/profootballtalk.nbcsports.com/2018/01/02/beating-a-team-three-times-not-as-hard-as-it-sounds/amp/