Yep, the chat log backup basically renders WhatsApp completely insecure. They also constantly nag you inside the app to enable it. This is how they caught Michael Cohen (and presumably others). Unfortunately Signal does it, too.
Yes, you're given a random password when you enable backups that you need to use when restoring. They don't get uploaded to the cloud. On iOS there's no backup feature at all AFAIK.
At least on iOS - whatsapp doesn't seem to nag about backups (i don't think i've ever enabled it), but you can do a local backup/restore if you replace handset. Signal encrypts your chats locally (but not binary blobs/video/images) but they cannot be backed up and restored locally.
