What I was wondering about the fact, that only lowres copies of the photo is copied rather than an exact copy like it is used to be in all other UX cases.
It's not a "lowres" copy, it's a lower resolution copy. And it is not the same as any other UX cases, you just assume it is.
The problem is that you've not grasped the nature of iPhoto, Photos, Aperture (and indeed, Lightroom). These databases make vast use of virtualisation - that is, they make all changes virtually - the original file is never changed - and that's why you can go back to the original image at any time. So the image is a different thing from the file, particularly if there have been any edits on it. The only time a change is committed to a file is when it's exported.
Exporting is tedious to do if you do a lot of it. There are a lot of options in the export panel, and to have to reset them each time is boring. So, for those situations where a 'good-for-most-things' version of the image will do - if you're dropping into a Word Processing document, an email or so on - they use the Preview. It's convenient. It's easy. And, frankly, it works for most people in most cases. In fact, you didn't even notice the difference.
If you want to edit the original in another app then each of these offer ways to do that without exporting - external editors in iPhoto, Aperture and Lightroom, extensions in Photos. They allow you to round trip from the database to the other editor and back.
Finally, then you can simply export, in a variety of formats and qualities from each of these apps.
All that's happened here is that you've made a guess at how these apps work and you've made an error.