As a Kindle user, I still miss the old version of the site. The new one looks great on normal desktop, but the old one was simple enough to load and directly download books on the device's built-in browser.
• On the one hand, E Ink devices have a fairly known set of limitations, and it would be ridiculous for me to expect them to render the whole web well.
• On the other hand, it's good for website designs to consider the kind of devices employed by their users. Using a Kindle to access Gutenberg is likely less of an edge case than it would be for other sites, so it's worth the extra design work.
(Keep in mind that -- given my sibling comment -- this is all theoretical. The latest iteration of Gutenberg's site is much better than the previous version)