Yep. Exactly.
And breaking free of the walled Kindle/Nook garden is similarly out of reach for about the same number of people that don't care about Apple's walled garden, which is the majority.
Again, they literally exist in every corner of our lives, and the 99% of consumers/normies don't care.
The "walled Kindle/Nook garden" isn't similar Apple's ecosystem. A Kindle or Nook will let you access it's EMMC and put Epub files or PDFs wherever you need to. It functions indistinguishably from a store-bought file and doesn't even make you enable Developer Mode to get there. It's "out of reach" in the sense that you need the skills to follow a Wikihow article to do it - my grandma could figure it out.
iPhones don't let you install IPA files on equal-footing as Apple, ever. That's the problem, and it's what the DMA remediates. I don't care how you or the normies feel about it any more than I consider the public sentiment towards Bell telephone or Internet Explorer.
This is incorrect. Modern Kindles classify books added as "documents" rather than books, which limits their features and treats them as second class citizens.
I doubt most people care, but you're not on equal footing to Amazon loading a book onto a Kindle.