This is not an anti-Kindle rant. I have purchased (rented?) several Kindle titles myself.
However, YSK that you are only licensing access to the book from Amazon, you don’t own it like a physical book.
There have been cases where Amazon deletes a title from all devices. (Ironically, one version of “1984” was one such title).
https://www.nytimes.com/2009/07/18/technology/companies/18amazon.html
There have also been cases where a customer violated Amazon’s terms of service and lost access to all of their Kindle e-books. Amazon has all the power in this relationship. They can and do change the rules on us lowly peasants from time to time.
Here are the terms of use:
https://www.amazon.com/gp/help/customer/display.html?nodeId=201014950
Note, there are indeed ways to download your books and import them into something like Calibre (and remove the DRM from the books). If you do some web searches (and/or search YouTube) you can probably figure it out.
Everyone should generally assume that unless you have something tangibly in your hand, you either do not own it or you may very easily and/or suddenly lose access to it. You could test this by trying to access the content without having to sign in to something.
All these streaming and subscription services should be considered ease of access conveniences. In other industries, you pay a premium for something to be prepared for you to consume. In the subscription industry, you’re paying less because you’re not paying for the content but for a license to temporarily consume the content (and probably because your info is being sold to advertisers).
Fun Fact: If you were to rip a Bluray to your computer, you’re legally not permitted to watch that movie if you’re no longer in possession of the disc. This is because you’re not purchasing the content of the disc but the license to view the content. Decrypting DRM is illegal not based on whether you own the content but because the DRM encryption itself is separately copyright protected.