You forgot the third and fourth failure modes: weight and bag space. Books take a lot of it. An e-reader is thinner than any book and weighs the same no matter how many it's holding.
I used to take my e-reader on field expeditions when I was an archaeologist. Never had one die or break even after months in places like Siberia. The number of notebooks that were ruined during those same expeditions is non-zero, usually from condensation or the physical trauma of a backpack.
Considering you're on HN, it's likely a safe bet to say you also travel with a laptop. In which case, an e-reader is still a waste of space because your laptop can just open ebooks too. Or if you don't, then your phone is still a better space saver for reading books with. Yet, you will likely prefer to take your e-reader with anyway (and its charger if it isn't the same as other devices).
This is why I find "saving space during travels" a very relative argument to make, because it's clearly down to preference.
Of course it's a relative argument. Everything is.
I don't personally travel with a laptop unless I plan on working remote. Too heavy/bulky and more importantly, you need to take them out going through TSA. The e-reader doesn't need a charger for the 2-4 weeks I usually travel. If I'm traveling longer, I'll bring a single additional USB cable (that will go away the next time I upgrade).
A phone doesn't take bag space because it's always in my pocket, but it's significantly less ergonomic and much less power efficient for reading. The value-add of being able to read without draining battery on my most important travel tool is worth it on its own.
My laptop and phone can't last through a long-haul flight. My e-reader doesn't need charging until I come home, fits in a jeans pocket and is a similar weight to my passport.
That's kind of my point - your preferences are to the advantage of the e-reader. For others, the same might apply to physical books instead, despite the disadvantage of bulk.
The ergonomics on any laptop is dogshit compared to a dedicated e-ink reader. Just the amount of brightness the display beams to your face makes it suboptimal for reading in low light.
And the "charger" I need with my ancient Kindle is a standard micro-USB cable, not exactly exotic. And as soon as this one breaks down, the next one will be USB-C like a good 90%+ of my devices I travel with.
I used to take my e-reader on field expeditions when I was an archaeologist. Never had one die or break even after months in places like Siberia. The number of notebooks that were ruined during those same expeditions is non-zero, usually from condensation or the physical trauma of a backpack.