Still more secure than non encrypted email yet a lot of people still use email to send fairly sensitive data.

Email doesn't go through an app controlled by Facebook so I don't agree about your security assessment.

You don't know where your email goes through, and email for sure is not end to end encrypted.

WhatsApp uses the Signal protocol. Closed source code can be decompiled, open source does not magically give you better security properties.

> WhatsApp uses the Signal protocol

claims to do so.

> open source does not magically give you better security properties.

Reproducible builds do, in fact I have no idea if you and I are running the same whatsapp at all.