Tolkien didn't write his book for young children. It's an epic tale, using time honored techniques to build suspense and dread over a long time period. I think late teens is about the earliest most would be attracted to it and understand it.
Harry Potter on the other hand, is a much easier read and isn't as heavy in the portrayal of the villains. Interactions are quick and sharp, and over in a few pages. It's well written and a great deal of fun. Much younger kids can read and understand it.
The author of this article might as well have said that submarines aren't anything as grand prix racers. Or that you can make better lemonade from lemons than apples. Both the Lord of the Rings trilogy and the Harry Potter series fit my definition of "classic".