I think the disconnect here is that at least for a large part of RFA/RFE's history, simply broadcasting fair and accurate news was effective "propaganda".

Whether that's still true today or not is not something that anyone here is going to agree on.

They never "simply" did this. They often did this, when the truth was good news for them, but so does RT.

The "Truth" (or facts presented in a very specific way) is a incredibly effective form of propaganda. You think foreign governments like Chin haven't been using the storming of the United States Capitol as a means to demonstrate the US's weakness or incompetence?

No one said that the U.S. doesn't engage in propaganda. But RFA News isn't it.

Why is it so difficult for Americans to believe

Suggesting that "Americans" suffer from a lack of introspection reveals your own biases. 350 million people. 350 million different worldviews.

So in your view as one of 350 million, RFA is only(or mainly) set up for providing news to brainwashed Chinese people but not promoting democracy and universal human rights value?

I said no such thing. You should not make assumptions about other people.