> Document navigation is absolutely a core part of reading.
This is a stretch. "Reading" means reading. You open a book and read it cover-to-cover. "Document navigation" is extra stuff beyond reading - it is not core. When you read a novel, you are not expected to jump back and forth between different chapters or sections, and the vast majority of people don't.
When you teach your child to "read", you don't teach them to click on PDF links (that's "web searching" or "computer literacy" or whatever) or to flip to arbitrary pages as fast as possible, or to search through a file - you literally teach them the English alphabet, how to parse words and sentences, and that's it - they know how to read. One knows how to "read" even if they've never seen a computer in their life, and if they don't know how to cross-reference books and articles, and if they don't know how to use an index.
> When I read a book, I page around it because that's how books work.
That's irrelevant. You can write on the margins of a book "because that's how books work", yet that's totally unrelated to "reading". I can clip out fragments of a book and put them on my refrigerator - that doesn't mean that a core part of reading is the extraction of inspirational quotes.
> When I reference a book I've already read, I want to look in the index or the table of contents and go there.
And yet, that's not a "core part of reading", and doesn't need to be optimized as such. The core parts of reading are reading words and flipping pages. Indices and tables of contents, while important, are not a core part of reading - they're important, sure, but if you remove them, you can still read things. That's what "core" means - "core" means "without this element, you cannot do the activity".
Let me repeat that again - if you remove the ability to flip to arbitrary pages (but keep the spot you were last reading in - which the reMarkable does), remove the table of contents, and remove the index, you can still read a book.
Will you be able to perform research effectively? No. But that's not what the reMarkable is for. I'll be the second to admit that the reMarkable 2 is terrible at research - but it's not meant to be used for research, it's meant to be used for simple reading, and note-taking while you do research on another device.
> [...] searching are core scenarios.
False. Their homepage literally never mentions "search" or "index". It's simply not there. Would search be useful? Heck yes. Is it necessary for reading? Absolutely not, see above.
As feature-limited as the reMarkable is, it is upfront about those limited features, and it executes on the features that it does promise at least better than most other pieces of technology.