Decent article but the author made an assumption that elevation isn't something to be concerned about by saying..."Elevation can be pretty simple to account for because gravity is a constant force for which we know the exact formulas". This is not a true statement.
But while gravity is a constant, elevation does have to be factored in if you're operating, or going to hunt, in an area with notable elevational changes compared to your regular home area. This is typical of the western half of the country vs. the commonly lower elevations of the majority of the eastern and southern parts of the country.
Lower altitudes and lower temperatures result in denser air, therefore, more drag on the bullet and more bullet drop. Conversely, higher altitudes and higher temperatures result in thinner air, therefore, less drag on the bullet and less bullet drop. This, and more explanations are from here...
On top of that add in the higher humidity typical of the east and south vs. the drier west with the exceptions of the western northern coast.
Another point that's MIA in this article is the effects of slope (inclination) on accuracy.
While not a big factor shooting at a flat range or "Flat" country, again typical of the majority of the eastern and southern parts of the country. But it's a serious factor n the mountainous west, or if your shooting at a range with targets set up on a hill side at various distances.
Together elevation and inclination have notable influences on accuracy where these conditions exist. And while the author touches upon "wind effects" one needs to consider the effects that hilly/mountainous valleys & draws can cause different wind patterns because the terrain can result in swirling and/or wind drainage coming through the path of the shot from rifle to the target at long-ranges.
So, while this article touches upon some basics the factors above need to be taken into account if you shoot in higher and/or mountainous country. An expensive rifle/scope and gear won't automatically correct for all this.