The title you gave the map still sounds like an overstatement. It's pretty good. Greatest, though? I, a casual observer, don't see that. The mapmaker talks about "basic geographical awareness", and he has some good points (like the population density one), but I don't see it as being this important. Is there really as big a crisis of mapmaking in the US as the article makes it seem? and is it as important? I don't remember encountering such a problem in Russia or having trouble orientating myself on any given type of map.
If anything it is very well designed and seems to take all the best lessons and practices of cartography into account. What is also good in my opinion about his map over the NG one, besides the decision to not color state borders, is how he managed to keep every city label horizontal, curve-less and rarely overlapping big roads. One can also see that he managed to make all the highways easy to trace and have each highway icon exactly on the highway. That sounds trivial but I speak from experience that just doing labeling properly and consistently can be an enormous task. To have a map that is thought out down to that level of detail for the entire U.S. without having major design flaws is definitely worth something in my book. I agree that 'crisis' is a hyperbole. But the art of cartography has been getting less and less appreciation in the last decade or two. It's been so easy to make an okay map that barely anyone takes the time anymore to craft a great map.
To me this is like saying, "Why did you rebuild this sports car? Normal cars get the job done fine." Or one I've been personally told: "Why install a custom OS on your phone? It worked fine before." You may not see these improvements as important, but to someone with a passion for maps, it may mean a lot. I find that kind of passion for almost anything admirable. This guy hand-built a thing better than can be bought by map companies. That's pretty cool, even if you don't care about maps (I can't say I have a passion for maps, either). I couldn't give less of a shit about cars, in fact I hate them, but if someone custom built a car as a hobby exactly the way they wanted to, I would think that was really cool.