But, to me anyway, that wasn't the dumbest McGuffin in the movie. That was the Rich Purnell Maneuver, whereby the Hermes mothercraft is slingshot back to Mars to collect Watney. The story takes place in 2035 and that's important.
The Mariner 10 probe was the first spacecraft to use the gravitational slingshot effect to reach another planet, passing by Venus on February 5, 1974, on its way to becoming the first spacecraft to explore Mercury.
The movie shows Purnell sitting in a cold room with hundreds of servers connected to his laptop, ostensibly to do the harder than hard calculations. Give me a break. NASA had a 60 year Rip Van Winkle moment?