That is simply not correct. With properly implemented E2EE, you can communicate confidently over a completely insecure channel. You could post the entire data stream publicly on the internet with no loss of privacy.
I would still assume that with apps like Snapchat, there are inherent problems on meta-level (from an E2EE view) because for the users, Snapchat is essentially a trusted third party, providing governance/management features. But it can well be that Snapchat does not provide E2EE; I cannot see any remarks about it on their webpage.
"WhatsApp _considers_ chats with businesses that use the WhatsApp Business app or manage and store customer messages themselves to be end-to-end encrypted."
And later, they write that in many cases, Meta can actually read the messages.
