Don’t throw away your Kindle, Jailbreak it and take back ownership. Make your Kindle even better with KoReader and other apps. If you wanna see whats possible i recomment this Yt video. If you wanna get started here are all instructions: https://kindlemodding.org/ Don’t let it scare you it seems complicated but its just a lot of (easy) steps. So definitely possible in <2h.
I’ve found the quality on Gutenberg varies massively - since an epub is basically a zipped html file, I’ve had plenty that are just barely-converted text files, with problems like incorrect character encoding and that everything’s one big chapter.