I can only violently agree with the author: koreader is incredible. When I look for ebook readers, running koreader is an absolute must. The nicest thing about it is how hackable it is, since most of it is written in Lua. When I got my Kobo Aura One, koreader did not yet support the colored background LEDs, and adding support for that was actually pretty easy. The koreader developers are incredibly helpful and it's just a great project.

I've read for hundreds if not a thousand hours on my Kobo Clara HD. I've never heard of Koreader, but from what I see it seems only really useful for PDFs ? I never read PDFs, only epubs, and it looks like on Koreader I would be missing stuff like chapter progress, length to read next chapter/rest of the book, marking finished books, etc.

Am I wrong in thinking all these quality of life things for simple book reading are not present on Koreader ?

Where are you getting that from? The github repo (https://github.com/koreader/koreader) lists many supported formats and features, including epubs.