Are you sure about that? Even Amazon's own sales page state: "Kindle Format 8 (AZW3), Kindle (AZW), TXT, PDF, unprotected MOBI, PRC natively; PDF, DOCX, DOC, HTML, EPUB, TXT, RTF, JPEG, GIF, PNG, BMP through conversion; Audible audio format (AAX). Learn more about supported file types for personal documents." implying that ePub only works through conversion. They don't support DRMed ePubs through conversion either so it's a bit odd they say that instead of including it natively.

As I said, anecdotally I've already done it. Amazon only just enabled the PC "Send to Kindle" to support ePub directly instead of the old silly work around of rename the .epub to .kfx (and no other change). They've been very bad at keeping their list of formats up to date in their own documentation. Some of that perhaps because they don't want it to be so obvious and it is intentional obfuscation (to keep people using their store rather than going elsewhere for books), some of that because a lot of their kindle documentation seems to be in a "isn't broke, don't fix it" frozen state for years at time. You'll also note that the text you found doesn't mention "Kindle Format 10 (KFX)" at all and also you might notice that TXT and PDF are mentioned on both sides of that text as both "natively" and "through conversion" which seems to imply the original text was from the era when they were converted and they were added to the "natively" side later without remembering to clean up the other side. (They both have native support today.)