the themes are literally not there.
I mean, I guess that's true in the sense that themes can never be
literally there, uh, but if you mean whether the film
has themes, it has many, it just doesn't distill a complex real life into a cartoony slogan or crystalline scene... even if that's what genre film has programmed us to expect.
This was a cinema vérité slant, instead of "hit all the comic book movie check boxes (even if we check some)", which doesn't make it inherently better or worse, just different.
they kept revisiting this "will mankind trust him?" thing over and over just talking about it and then they do...nothing with it.
They do plenty on a personal level because it's Clark's story, not the world's. We still get glimpses of that with the markets freezing, the universal press coverage, etc, but that's not the story... there is no monolithic "mankind", mankind is made of men, so that theme is revisited again and again through individuals.
The reason the bully flashback occurs before the talk with the priest is because Clark's wrestling with whether humanity is going to turn on him. The bully is their capacity for evil, Pete's extension of compassion is their capacity for change, and his father reminds him of the choice... that it isn't a given, an assumption, or effortless default that Clark's going to be good. This is turning over in his mind when he uses the priest as a sounding board, who shows him trust in return by not freaking out or pushing an agenda on him. Clark doesn't give him much time to do much more than toss a slogan at him, but it likely affirms what Clark was already going to do.
Superman takes the leap and then the microcosm of humanity he is interacting with- the military- go from "shoot on sight" to "this man is not our enemy" to "team up against the enemy" to "entrusted to act as liaison to Washington." That theme of winning people over is a common modern Superman theme and doesn't just take it for granted that a single public rescue means an adoring public.
"Are you effing stupid?" is a remarkable sign of trust. You don't get to say that to Zod. Hell, you probably can't even say that to your boss.
It's nowhere near as crystalline as "Why do we fall?" or "With great power..." but I'm okay with a different take which tries to avoid those kinds of conceits.