His narration carried the film to it's conclusion and helped to (in my view) better tie up the themes of friendship. Older Spock talked with Younger Kirk, and Older Kirk (via message) talked with Younger Spock. Informing both younger selves of what the other would come to mean to them.
It's a shame we never got that, because I think it was damn compelling.
I don't understand the concept of Kirk&Spock deep friendship due to "destiny".
If nuCrew should have nearly the same destiny as prime Crew, then why nuSpock is so emotional (he even screams!) and his girlfriend is Uhura? If so, then nuKirk and nuSpock may have their own destiny without inevitable and obligatory friendship (bromance).