I owned a Kobo Glo and Pocketbook Touch, and I preferred the Pocketbook, because it allows to install koreader as a application into the stock firmware, while on Kobo you need to quasi dual-boot your system into koreader or stock firmware via a menu.
In my experience koreader integrates much better with calibre and allows managing my library with a filestructure. So that is a requirement for me.
Also the stock firmware on the Pocketbook was able to deal with my huge epub archive, because it didn't require indexing the library on the device, which Kobo struggled with.
From that experience I would pick a Pocketbook over a Kobo.
IMO Kobo is absolutely built to be a "better managed library experience" than kindle - but as you say other platforms are better if you have a large non-drm'ed library. Unless you plan to buy books from publishers / use the overdrive (now Libby) system, I do think a more user-focused offering like Pocketbook will be better.
I think this is a place where some regulation could do a world of good. I wish I could buy any ereader I want and shop at any bookstore I want. I wish publishers were forced to respect first sale doctrine on digital goods.
I fully agree! I'm also disappointed (but not surprised) that kobo (or some other 3rd party epub seller) hasn't created an API where you register a key pair (or whatever) and can decrypt books on your devices. I suspect it's based on publisher demands. Ironically, this is one place where a blockchain might be useful - sales are recorded on it, contracts are written with respect to it, and if the publisher goes belly up users can run nodes to maintain it.
There are multiple ways to install Koreader now. I think the most common is to use KFMon and NickelMenu which installs the quasi-operating system into a book in your main menu.
In my experience koreader integrates much better with calibre and allows managing my library with a filestructure. So that is a requirement for me.
Also the stock firmware on the Pocketbook was able to deal with my huge epub archive, because it didn't require indexing the library on the device, which Kobo struggled with.
From that experience I would pick a Pocketbook over a Kobo.
But maybe I should give Kobo another look.