"In what we believe" -- does the initial position of the preposition really sound better?
As I understand it, the rule that sentences or phrases should never end with a preposion is an over-simplification
a) I'm right and the first version results from blindly trying to adhere to the "rule".
It would be more correct to call it a guideline instead of a rule. It's a matter of preference, and what sounds best.
For example, "In God we trust" sounds much more official than "We trust in God". Both options are grammatically valid, but they carry a slightly different tone (in regards to in/formality).