I guess then the question for the people that are for the latter option would be:
Would you list Earthquake as a Related Move for Earth Power? Even though one is special and the other physical, they both serve basically the same purpose on a moveset, and are the most used Ground-type attacks along with HP Ground.
Remember, we can't be Pokemon specific when we do these.
Also, how far are you willing to go with the Related Moves? Is there a barrier when you'd stop listing certain moves? Such as, would you list Surf and Hydro Pump as Related Moves to Water Pulse, even though there's a drastic power difference between the two? What about Waterfall?