but they have the keys, and can't be trusted

They could still extract keywords on the sender or recipient device and send them independently of the message; the message is still encrypted but keywords such as “buy” and “house” were submitted to Facebook anyway.

I don’t buy the “end to end encryption” argument. If the app used encryption for the benefit of their users it would absolutely make no sense for Facebook to buy them for billions. The reason FB did so anyway is that they have a workaround the E2E encryption like described above.

Does WhatsApp make it clear what "end" means and how many so-called "ends" you are transmitting a message to?

...unless your software keyboard is logging your keystrokes and sending those home.