I'm sure Boruto is totally replaceable there. Even Sasuke could've pulled something out of his own powers, his rinnegan or something.
As I said, it is Boruto's movie and he's lucky plot needed him to be there.
With whom? Who else uses a power similar to disappearing rasengen that caught Momoshiki off guard? Yes, Boruto is just a kid and needed help and tips from his teacher and father- if he didn't need any, we could be complaining what a Gary Stu he was.
This chapter sets up Boruto as the protagonist -
Boruto brought in invisible rasengan- his very own tech.
He was able to handle the large Rasengan Naruto made and throw it properly.
Momoshiki's spirit acknowledged his potential and role in his defeat albeit grudgingly and cursed him along with the mark. We will see what it means and what that mark is later.
Seeing future/fate- that's hogwash, IMO. All of them claim but neither Neji, nor Kaguya nor Momoshiki could really see it. They can guess the potential and come to a logical deduction at best. They may choose their target and set things up, manipulate people in to doing something or refraining from it, but that's all.