I think you’re confusing your own file backup practices with ownership. If you purchase a DRM-free piece of software (say, a game from GoG), I’d say you own it just as much as if you bought the same game on a CD (assuming the CD was also DRM-free).

If you don’t keep a copy of the game yourself, and one day you can no longer access it because GoG ceases to exist, that doesn’t mean you never owned it. It just means you failed to back it up. You could also fail to backup a CD when it inevitably stops functioning.