I agree purely looking at tempo variation isn't everything, but I think perhaps "Zero tempo variation is a necessary but not sufficient indicator of "gridifcation" is closer to the message?

More specifically, they define gridification as: recording multiple takes, nudging every single note onto the grid for each one, then selecting the best take section by section (however small those sections are) so that every single note is absolutely perfectly on time, in tune etc, loses... something - it removes some of the humanity. The author also explicitly cites many other kinds of recording and editing as NOT gridification - e.g. playing to a click, using a drum machine.