If only they had explicitly defined how they will be using the word effort for the rest of the article, to address exactly this obvious and silly reaction.

I read the article before I commented, and I reread the definition just now, and I still think that effort/exertion/tension/whatever you want to call it, is a necessary stage along the journey to mastery. Maybe Mozart or whatever preternatural prodigy from birth managed to fit this stage into preconsciousness, but I can virtually guarantee that Katie Ledecky had to over-exert in order to build herself into the powerhouse she became. There is no way she expended "zero effort", either by normal use of the word "effort", or by the definition in the article.