Yes you kind of "own" your ebook, but.... The company that sold it to you can remove it legally form their listings, taking away your ability to download your book.
That's not what I'm referring to. If you have an epub or similar file, you own it. You can store it, and delete it at your own whim.
Yes, but computers are prone to failure, you are depending on a device to hold all your media. I've had backups and backups of backups, still losing things to failure. My books take up space, but they will be there unless my home burns down.
And if you store it in the cloud, and in thumb drives, they will be there even if your home burns down, and far more of em too.
Not necessarily, you can self-host. I also listed it as a backup, for actual storage on thumb drives, SD cards, etc. It's really not difficult, files are far more secure and safe than a physical book, which itself degrades upon use.
You have to pay to self host, you have to pay for cloud storage. I am not going to pay to keep books, I buy books and put them on a shelf. I can pull one off and read it when ever I please, I don't depend on any devices to read them, and I like it that way. This is how I feel.
You're fine to prefer that way, but you're just wrong about files being less secure or somehow less owned than physical copies.