WhatsApp is great for casual users but not truly end to end because of its design imo. Silent rekeying is the default behavior. No perfect forward secrecy here either: old messages silently re-encrypted with the new key and re-transmitted. The Guardian and others reported on this some years back and of course you can witness the behavior yourself if you flip that setting in your client. If a buddy gets a new phone, it will now disclose that to you (but not wait to send old messages). Was that really my buddy's new phone or an attacker? Hopefully I can trust WhatsApp (but trusting the broker means it's no longer E2E).

Yes, like everyone says it's all about your threat model. If it really includes nation states, you should not use WhatsApp. Everyone else can use it for iMessage like functionality over-the-top.