WOW!! Is this filesize argument like a guy thing?
I can believe you can get some really huge ebooks, I'd just never read them.
I don't want to get a Sony as 1) I don't like the UI and 2) Sony is treating their ereader like an unloved stepchild, which to me means lack of support. Kobo's crappy support is bad enough, at least they recognize that they are responsible for it.
I have a Kobo, which is the ONLY other epub using device here in Canada. I don't want to read on a tablet as I am susceptible to eye strain, my ophthalmologist is pleased I read on e-ink instead. The ONLY reason for me to buy the Kindle is because I want stability and decent customer service. I doubt very highly Amazon will abandon Kindles entirely, EVER. Yes, I'd have to convert my epubs to mobi or azw3 (which as I saw are NOT smaller), but I'll do that for stability and support.
As for the argument of sticking thousands of ebooks onto a reader or sd card vs computers and cloud storage, everything you say makes perfect sense. BUT, what you are arguing against is an urge or NEED to have that many on the reader or card, kind of a mental issue - I fully admit to having a form of OCD about having a lot of books on my reader. In *my* case, it doesn't make sense, it's not logical, but as with other forms of mental illness it's not something you can convince someone out of. If it were, my mother's house wouldn't look like something out of "Hoarders". I'm just fortunate mine runs towards loading up ebooks onto my reader and not my house full of crap.
More logically based argument, when I accidentally damaged my previous XHD, I lost all the ebooks that were NOT on my micro SD card (luckily that was not a lot). I simply removed the card from the reader and copied over what I had to my laptop, then to the new XHD (at the time Kobos did not automatically delete the book from the card as it does now). As I now have about 12G worth of ebooks that can't be done, but I keep redundant copies on 3 regular SD cards, my laptop AND two 2T XHDs. And DVDs.