The messages are encrypted end to end so compromising push notifications doesn't get you anything. That's the problem with this bridge, it adds a new server with access to the unencrypted messages.
edit:https://www.huaweicentral.com/new-whatsapp-report-feature-wi...
If they were going to look at all your messages, of course, waiting until the end user gets it is somewhat unnecessary, they could just get them straight from the sender since they're both "E's" in the e2e. But that's true of any messaging client. Unless you're inspecting the code and building your own binaries, you either have to choose to trust what they're saying or not (or I guess just don't care if it's not relevant to you). But again, that's not WhatsApp specific.