The idea behind this "documentary" is that Batman is modern mythology, Jesus is mythology, and so they are equal on every plane, making Jesus just another story. They even have a "First Council of the Bat" to comment on the Council of Nicea, where fans are brought together to determine what is canon. Batman is also presented as religion in and of itself in order to better drive the point home.
Ignoring that there are several different levels of canon when you're dealing with Batman (movies vs. comics vs. cartoons), the logic here is spurious at best. There are a lot of historical inaccuracies, as well as conflating a lot of stories.
The really weird part is that no one form the opposing side is consulted; this is presented solely to demonstrate that Jesus is nothing more than a mythological construct and is therefore of no consequence. It just comes off as assuming that all believers treat The Bible as a historical document, something that is hardly universal.
If you believe that anyone who believes in religion is mouth-breather incapable of any form of rational thought, this is the movie for you. For anyone whose thoughts on religion have any kind of nuance whatsoever this is probably a solid miss.
