This article is poorly articulated (consider the definitions/categorizations for amateur, professional, scientist, genius, and pre-med.) Even the example does not clearly show his point. Is it "genius" to consider that spectral intensity changes gradually rather than suddenly?
Anyway, I get the point because it's mundane and everyone's thought about it before.
I don't think amateur-vs.-scientist-vs.-genius is a very good set of names for the distinctions he is trying to make, especially if you're going to reach back to Herschel's time. To pick some influential folk who fit into that period, consider Babbage, Darwin, Mendel, Pasteur, Boltzmann, Cantor, Semmelweis, the Wright Brothers, and Wegener. Consider also their rivals and critics. (Since I included a number of controversial folk, various of their rivals and critics are still remembered.) We can come up with generalizations about what the influential folk did right, but I don't think it works to say that, e.g., they were scientists while their critics and rivals were amateurs.
Or consider all the advice in an essay at the level of Hamming's "You and your research." It doesn't seem to me to be useful to try to boil down the multiple properties discussed there into boolean predicates "is this person a scientist" or "is this person an amateur," or even to try to choose particular points in those multidimensional property spaces as typifying "scientist" or "amateur" or "genius."
I wholeheartedly approve of people writing about some of the principles in this essay, notable the ones often summarized as "genius is 99% perspiration" and "a month in the lab can often save a day in the library." Those are very important principles, and very often people don't appreciate them enough. But trying to define the amateur/scientist/genius terminology on top of those principles doesn't seem very sensible.
"In the 4th century BC, Aristotle asked why the heat of the sun prompts us to sneeze, whereas the heat of the fire does not. A partial answer came two millennia later, when the English natural philosopher Francis Bacon showed that his photic sneeze had nothing to do with heat at all: if he closed his eyes when going into the sun, he didn't sneeze even though the heat was still there. While Bacon's application of the scientific method was beyond reproach, his conclusions are distinctly iffy to a modern nose. "The cause is not the heating of the nostrils," he asserted, "but the drawing down of the moisture of the brain."
Anyway, I get the point because it's mundane and everyone's thought about it before.