That is a novel and quite broad interpretation of E2EE. In typical E2EE only endpoints of a (logical) communication channel can decrypt messages on that channel. But E2EE does not say anything about what an endpoint can do with those messages once they decrypted them -- they could print them at the public library and leave them there, they can forward them to the FBI, they can post them on reddit, etc.
If you do not trust your communication partner to safeguard your messages, E2EE will not help you at all.
The point is that many people have iCloud Backups enabled without any awareness whatsoever of the implications, as iCloud Backups are opt-out and there is zero disclosure within the OS (only an Apple Support webpage nobody will visit).
It leads to E2E being systemically weakened, since most of your iMessage conversations will get immediately scooped up by Apple and alpbabet agencies, dragnet-style.
I understand that, I didn't mean the concept of e2ee requires the endpoints to never share it at all. What I meant was, commonly people will disable iCloud backups hoping to regain some privacy, but it does nothing because most of your communication partners use iCloud backups. Just like people who switch to eg. Protonmail - if you only ever talk to GMail users, it doesn't really give you much extra privacy.
If you do not trust your communication partner to safeguard your messages, E2EE will not help you at all.