> default zero-effort privacy for the ignorant. (Which WhatsApp does pretty well for example.)

Can you elaborate on what default zero-effort privacy for the ignorant WhatsApp offers, that Signal does not?

I don't know, I'm not familiar with Signal. But features such as described above with worse privacy than the basic chatting functionality detract from it, it's not just that it would be a bonus if it were better, because that's exactly how effort comes in, having to know about it, and the typical layman user just blindly uses it.

Take Telegram for example, where only explicitly 'secret' chats are e2ee, you have to go out of your way, it's not the easy path.