Personally I completely agree with you, and could have written almost exactly that paragraph - I too have a ReMarkable (the 2nd / current version), and love using it as it ships for both note taking and especially for reading ebooks/PDFs ("especially" just because it's what I use it for more, not because that's what it's better at - in fact, its UI for reading documents is among its weaker points and I hope they improve it in future software updates).
However it is worth pointing out that you can SSH into it, and there are a fair few 3rd party tools and hacks for it - so far I've avoided trying any of them as there's nothing that I want strongly enough to have even a 1% risk of bricking it to worry about. But I'm tempted to start playing around with it someday.
This is the best list of stuff for the ReMarkable that I'm aware of, though I don't know how complete it is / how many released tools or guides there might be that aren't included here: