The biggest security issue on WhatsApp are the backups, especially the cloud backups not the protocol and this so called "backdoor" itself. Pictures not encrypted on backups, encryption keys of backups stored on WhatsApp side which might or might not (???) have access to your cloud backups on Google Drive and iCloud. If a government (USA?) gets access to one of your or your friends backups and the encryption key it can see all of the conversation. This is for me the weakest point of WhatsApp.