Failing to connect those dots is (unfortunately) what keeps many, many people from moving their otherwise private conversations to a more private channel. I think you're right that it bears mentioning.
Many people are absolutely convinced that their phones are listening to their in-person conversations already, yet seem ok with continuing to use them.
Definitely Signal. It strikes the fairest balance between industry-standard end-to-end encryption ('E2EE') and usability.
Get as many of your contacts onto Signal as you can. Disable the displaying of message text within device notifications from within the Signal app settings (for both Android and iOS).
GPG doesn't support forward secrecy, which is table stakes for encrypted messaging these days. And that's to say nothing about the slightly suboptimal usabilty...
True, but you're not trusting any corporation to do what they say they are doing, or not changing it out from under you. I guess you're trusting the Gnu people though.