AFAIK when you use "send to Kindle", Amazon takes your epub and runs it through Kindlegen (or whatever Amazon's current equivalent is) to create an azw3 on their end. They are not rendering the raw epub - it goes through a black-box conversion before you see it. Thus, all bets are off as to how the "epub" will look on your Kindle. (Indeed, Calibre does a better job converting to azw3 than Kindlegen! That's why we use Calibre when creating azw3 files at Standard Ebooks.)
I won't believe Kindle supports epub until I can transfer an epub via USB cable and have it available to for immediate reading. Anything else is Amazon "supporting" epub with very big air quotes.
"We wanted to let you know that starting August 2022, you’ll no longer be able to send MOBI (.mobi, .azw) files to your Kindle library."
That said, that was August 2nd and sending that file as MOBI did work.
(And the success e-mail message they sent me today said they did convert the Man and Superman EPUB to "Man and Superman: A Comedy and a Philosophy.azw3".)
I won't believe Kindle supports epub until I can transfer an epub via USB cable and have it available to for immediate reading. Anything else is Amazon "supporting" epub with very big air quotes.