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I feel the same way. Just build an independent app already. Telegram did it well. What's stopping WhatsApp ?
As kawera said two comments above yours: Their servers do not store unencrypted messages so they need to come from the phone. ---- That's why some people criticise Telegram: Their messages have to be stored unencrypted for their setup to work.
It seems like there should be ways to do it without storing unencrypted data.