It's not being hyped, you are just over-reacting because it doesn't meet the use case you'd prefer. It's not a security feature and it's not about privacy. Clearly, like PGP of yore which had view-only messages, one can simply copy (perhaps screencap in this case) the message and then do whatever.

This is an augmentation to what postini had, and now in core G Suite, of defined retention periods for email. Now, users can make one-off decisions on a per-email basis.

It's like the secret discussion/chat system that uber uses, I can't find the name, that guarantees protection against legal discovery by encrypting the chat and making sure it is ephemeral.

There are valid (maybe not morally, but legally) reasons to have defined retention periods and this is a nice addition to that.

It does bring Google into the Apple privacy-is-our-business sphere in that cooperating parties that solely use gmail have much better assurance that they don't leave traces behind.