The counterpoint is that it’s unlikely you’ll switch to replying to poorly thought out comments on hackernews, for an example, when you’re on a dedicated reading device than when you’re on just another app on your internet connected attention thief of a device.

That is a reasonable concern, but it varies based on the person. I'm not worried that I'll suddenly start browsing the internet while reading on the subway. It's not at all unlikely that I'll suddenly interrupt my reading if I'm messaged while I'm on the subway, but that's something I consider desirable, not something to be avoided.

Cool. I do have it on my iPad (tablet) to read when I forgot my kindle. It hasn't happen in 3+ years. However, I forgotten my iPad a lot of times and not my Kindle. :-)

My phone (iPhone 11 Pro that will likely last for 2+ more years) is just a really good camera, that has some phone function with the usual calendar, maps, etc. I avoid phone calls as much as I can.