View from the faculty POV: I taught mathematics as an Assistant Professor at Harvard for five years (2000-2005), and this advice seems wrong. It’s very generic and abstract, whereas the actual mathematics department (students, faculty, preceptors) at Harvard at any point in time is made up of real people, most of whom are really interesting fun and genuine math loving human beings. I guided dozens of students in seminars, interesting math research projects, and much more, and many of them really benefited from the environment and went on to truly love mathematics as a long term career.
If you can get beyond the clickbait title - I think what you'll find is that Gladwell is really talking about the very real STEM people, most of who are really interesting fun and genuine math loving human beings - who were weeded out in Freshman Calc BC or Differential Equations because the bar is so tremendously high if everything is graded on a curve at a extremely selective university - before you had a chance to meet them.
I agree, even as OP. Malcom Gladwell's writings on elite universities have gone viral, and even though some good points are sometimes made, many are just stretching the truth for clicks.
As for the general grade inflation problem: It is confusing that Harvard's grade distribution is so different than schools with similarly strong student bodies like Princeton, Columbia, UChicago, Berkeley, etc. Especially very, very large portion of students are legacy / recruited athletes / very wealthy donor parents. According to the affirmative action lawsuit, over 10% of the student body alone was on the "Dean's interest list," a very elite group of autoadmits, for example.
