[Caged Great]

I thought that Jon would not be the one to kill the Night King. It makes sense because it would be so telegraphed. Like Beric, he was brought back to play a part.

I'm of the belief that Bran being the 3 eyed raven is also the lord of light. He foresaw that the only way for the night king to die was for Arya to kill him with the catspaw dagger. He/lord of light needed certain pieces to be in place in order for her to get to her goal. It was the only way he'd die.

Beric needed to provide space for her to escape the dead in the hall to get to Melisandra. He kept getting brought back because he was needed to be that Berricade.

Similarly if Jon wasn't in the courtyard, then Arya couldn't get passed the dragon as the dragon would have seen her and that would have been it. The night king needed to view Jon as the true threat and would have been focusing his dragon's attention on him. Not some small girl. Jon screaming what sounded like Gooooo go go makes sense. It created that small window for Arya to sneak through, run like hell and do what needed to be done. As for the time it took, it's only about 40 feet or so from the courtyard where the dragon was to where Bran and the Night King were. Doesn't take that much time for someone to sprint there. Because of the Night King's hubris, he didn't take her seriously. Much like Oberyn after he defeated the mountain. Let his guard down and it was the end of him.