WhatsApp is arguably more secure than many of the alternatives. Just look at the repo for Signal. For privacy it probably isn't, when you're in the US, that is.
Metadata-wise, yes. For protecting content, it's still pretty good. Also, WA seems to add features pretty close to Signal, which could indicate WA supports Signal in testing some of the features Signal provides consultation wrt secure implementation. WA probably doesn't want to fully take the wheel and fuck around with the Signal protocol. They've of course made some changes such as the group management system, and the levels of safety number warnings (no-warnings/non-blocking warnings as opposed to Signal's non-blocking/blocking warnings).
But WA has been working on interesting proof of concepts for wider deployment such as the client-side encrypted backups. Those are actually fantastic when properly implemented. There's of course shitty aspects with WA about those like the 64-bit passwords, but, if that's a feature Signal thanks to possible collaboration can properly deploy later, I'm all for it.
There's a difference between Signal being categorically better for pretty much everything when compared to WA, but, WA isn't the worst option, even when considering its owned by FB.
WhatsApp is arguably more secure than many of the alternatives. Just look at the repo for Signal. For privacy it probably isn't, when you're in the US, that is.