WhatsApp could exfiltrate messages at the ends. But I assume the trick lies in the word "default". Didn't Skype also default to end-to-end encryption, unless there was a server flag that disabled it for that specific user (I might be fuzzy on the details)

Every encryption is end to end if you're not picky about the ends, or metadata.

Do you trust facebook (excuse me, meta) to not snoop on your messages, and to not share them with the "intelligence" agencies ?