I don't think the numbers in the article are flawed at all, (most people, like the 2nd poster, believe it is a bit dramatic) the author says in the paragraph preceding his calculations, changing 50% per week, (and many aquarists think that is a huge water change (and most, at best change 20%-30% per week)) will "not" be sufficient,
and I agree, if you want what I consider a safe nitrate level.
But the toxicity of nitrate is to some, debatable.
To me, it is not, and I, in my 20%-30% per day daily water change routine, change over 120% per week.
And use pothos, and planted refugiums.
Still my nitrate concentration hovers at 2-5ppm.