That said: Neither is mail.
Mail is still useful for a lot of things.
See also tptaceks take:
I'm comparing it to mail.
And if you want a more secure alternative, please go with Signal.
WhatsApp leaks metadata east and west, and if you or any of the people you talk to enable backups all your chats end up in the cloud with a different company.
So much for bulletproof encryption in that case.
Whatsapp backsups are strongly encouraged by the app on a frequent basis. You cannot control the backup settings for your contacts. Therefore almost every group is backed up to google drive. Google has allegedly given this data to the authorities because these chats have leaked in a popular case here in India.
https://www.thenewsminute.com/article/how-ncb-retrieved-what...
https://www.indiatoday.in/technology/news/story/bollywood-wh...
This is not a problem that Signal faces as they do not keep any of your data.