I tend to disagree, or at least argue that UI/UX is strongly subjective. I have sought out digital copies of books that I have in paper form just because I strongly prefer reading on an ereader for text. Obviously, something with graphics is likely to be better in paper.

You can't lose your place easily. Lighting isn't an issue if you buy a backlit model. Reading lying on your back or side is much easier. Traveling is easier with an e-reader. Access to wikipedia and the dictionary on the same device.

There are emotional reasons that I like paper books, but if I'm just trying to read, give me an ebook.

Ebooks will be on their way to being a match when readers come with facing-page screens, spine and cover screens (I've forgotten the authors of ebooks I'm actively reading because I don't get reminded of the title & author passively by just having the book around me) and some kind of much better interface for locating and bouncing between bookmarks, which interface will probably need to not reside entirely on the main screen(s) in order to make a real difference. Still missing a lot, but that'll close maybe half the gap.

To add to your comments on travel, reading position, lighting, some books are just too large or heavy to lug around or even hold for long periods. There are a number of door-stopper books that I otherwise just wouldn't have read because of this.

If the medium makes the difference between me reading a text rather than not reading that text, I tend to think that makes it functionally "better".