"This was written down for us by a guy who was in the room when it happened." It is extremely unlikely the author was in the room that day.
Again, why did Stephen not even attempt to convince the Sanhedrin? "flashing neon sign" ... apparently it was not back in those days, let alone today. Imagine if early christians had such good evidence, how much faster and more broadly would it have spread if the Sanhedrin would adopt Jesus his views. Muhammad would have been devout christian.
"[..] That is, your presupposition is determining how you view the evidence."
That is true. But it is called the null hypothesis. Innocent until proven guilty. It is the number one "invention" that launched humanity into modernity. But that should not be misunderstood as not giving alternative hypothesis an honest look.
But the claim of something supernatural is quite a strong one, it should come with an equally strong signal before it becomes credible. As things stand today, the conclusion is, god is unlikely and unprovable. Moreover, belief in invisible unknowable things does not do the world any favors.
For the bible or christianity to exist, we do not need a supernatural explanation, it falls well within normal human behaviour.