Haha?
Del Potro won that much for a variety of reasons (working the backhand is included) but maybe you missed Murray vs. Federer where Federer’s backhand absolutely CRUSHED Murray’s backhand? There is ALOT more that goes into a stroke than racquet head movement. Go play competitive tennis for a few years and you’ll understand where I’m coming from.
In regards to Venus beating Federer with only backhands, this proves you have no idea what you’re talking about. None. Venus would be blown off the court by the power of Fed’s backhand.
Go play competitive tennis before lecturing people about inefficiencies. What is true on paper isn’t always true in the real world.
The laws of physics work the same way for tennis players as for other people.