Yes, it is, but unfortunately I'm not sure how to get around it in a system where you aren't actually buying the goods, but borrowing them and then they are required to know how much of it you used. Thankfully you can still buy books outright if you don't want to be tracked (sort of. All KU books are Amazon exclusive, so Amazon will at least track that you bought it).

That said, Amazon is already syncing your location,and any annotations you've made[1] so they persist across all kindle devices, so there's already a bunch of tracking in place. Given that there's already some tracking, I wouldn't be too opposed to a per-page bit for whether it was read, triggered when the page has been lingered on for five or more seconds (scaled down to 1 second for partial pages, such as ends of chapters).

1: Anyone remember the big episode years back over Amazon realizing they didn't have the license to a book, then removing it from all Kindle devices automatically, including the annotations made? In what is possibly the most ironic situation I can imagine, the book was 1984.