Many of the people who have created GPL (not LGPL) libraries would disagree. Strongly.
These files don't just contain "formatting information". They contain actual executable code created by Apple. Apple's claim lies on the distribution of their code, not your content per se. They can put any restrictions on the distribution of their code that they want, whether we like it or not (and I don't particularly like it myself). They're not claiming ownership of your essay. They're claiming ownership over the code they wrote, which their system uses to display it. Not the same thing.
What you, and others, are claiming is that this type of license has no legal effect. That's clearly wrong.
Let's not confuse the two issues of whether it's a good idea for Apple to do this (it isn't) and whether they're legally allowed to do it (they clearly are).