I don't know if I'm misunderstanding you, but tons of actual things don't belong to the person "holding" or using it. Leased cars, rented houses, work equipment, stolen items. It is a huge simplification saying that "anything belongs to the person holding it, except for borrowed items", which ignores a bunch of history and legal precedent establishing exactly what it is people mean when they say somebody owns something.
Your definition of data ownership certainly is a definition, but it's far from obvious or mainstream. If you texted an intimate photo to an ex, do you consider them as the owner of the photo, meaning that they're allowed to do whatever they want with that photo (as ownership typically implies)?
> Leased cars, rented houses, work equipment, stolen items.
Basically only borrowed and stolen. Stealing (actual stealing) is a crime by itself. And it doesn't make sense to borrow data. If somebody borrows you a song, you can just make copy yourself and the copy is yours. Which is how reality always worked. Didn't you have a casette player with two slots? Those weren't for playing two tapes simultaneously. Is the new generation so brainwashed by virtual world of fictional intelectual property, terms and conditions nobody reads and licenses which claim to be source of your rights and don't give you any, that they have forgotten how information exchange actually works in the real world?
> which ignores a bunch of history and legal precedent establishing exactly what it is people mean when they say somebody owns something.
I think copyright ignored more. And doesn't reflect reality on top of that.
> but it's far from obvious or mainstream
It's obvious and spontaneously created by anyone who deals with data and doesn't know or care about the (stupid) concept of intelectual property. "Do you have the file?" What does it mean intuitively? Yes, I have it. I can make you a copy.
> If you texted an intimate photo to an ex, do you consider them as the owner of the photo
Yes. Obviously. Just as much as I am. Thinking otherwise would be believing falsehoods about reality.
> meaning that they're allowed to do whatever they want with that photo (as ownership typically implies)?
They obviously can do with it whatever they want to. Are they allowed? Is the sun allowed to rise up in the morning? What's use there is to forbidding it?
They can do thousand copies or delete it from existence. They can modify it. Print it. Whatever.
When they publish it. Well, what happens next depends entirely about whether I'm entitled to protection of things I consider private from being publicized. Or if I'm protected from harassment. I might be or I might not be. However whatever protections I am awarded in that regard have nothing to do with general rules about the data. If I harass a person with a megaphone that I own it still could be illegal.