Pilot is not an uncommon term for guiding or steering any non-weeled or non-tracked vehicle type. It is typically used in most sci-fi and anime to that effect and that stems from the VERB definition of pilot. "To steer". A pilot steers a craft.
Athleticism implies piloting a 'mech involves... being athletic. It's a machine and whilst dexterity plays a role, there are degrees of intellgence and learning about the units systems that would be taken into consideration as well. That's why distinguishes 'piloting' from 'driving'.
See in aircraft where on top of your reflexes and what you can see outside the aircraft, you have your AoA, slip, artificial horizon, throttle settings, fuel settings, TFR, warning panels, radar warning receiver, knowledge of maneuvers, and host of other information pouring in at the pilot. Things that a "driver" wouldn't have to deal with an
that as a whole have only two things to do with being "athletic"
Complex military units with single pilots would have that same risk of "information overload" so pilot is certainly a much better term than driver, much less the jock-strap wearing "athleticism".
Hence why when in the Jet age the REO (aka GiB) was added to combat jets, the pilot was often jokingly called the "driver" as a lot of that work was taken out of their hands. It was in some ways a derogatory term in the mid '60's when they thought missiles would replace both maneuver and the internal gun, but pilots started calling themselves "drivers" as a badge of honor when it became apparent that you did still need the internal gun for when things go bits-up face-down, and that despite missiles range you still had to get the bloody things into "parameters" to fire.
I'm a former stick jockey -- "Viper driver" even -- I have ZERO problem with the term "pilot" being used for any single crew combat vehicle more complex than a automobile. It IS piloting, as in the act of steering or guiding. If the term pilot and cockpit were acceptable all the way back to Mazinger Z, it's good enough for us today.
Reminds me of someone getting confused by my use of the word predating --
as in the phrase "bootcrap is a bunch of nube predating bull****, go find a stick to scrape that off with before tracking it all over your website's carpets --- as in to prey upon, to act as a predator. Not as in "it came before".