As if there is just me and the universe, and if I have the correct beliefs, the universe will reward me, and if I have incorrect beliefs, the universe will punish me, on average. Therefore, let's praise the universe and let's have correct beliefs!

It is just you and the universe. "Other people" are a part of the universe.

(I actually kind of agree with you, though - the larger point is that your beliefs can impact outcomes directly rather than only via predictions. A non-sentient example of this would be Placebo effects. This seems not to have been included in the OP's discussion.)