When I download a movie this way, I truly own it. Same as I own a DVD disk. It’s just the medium that is different. E.g. I have a collection of Friends on disks, which is legal, I own it. But when it’s ripped as files and stored on an old hdd so I could rewatch some episodes just plugging the disk via USB. I assume it is likely to be illegal.
The thing is, copyright holders think it’s wrong, and they want us to rent the content, not own it. I mean it could be done other way technologically, avoiding physical medium and still making it legal somehow. It could be done if the party was interested in it. The problem is not in the physical medium itself.