Yes Bort being in a battle he was only in because of forced plot and main character privilege being able to defeat the villain once again because forced plot. He had that fight and victory handed to him on a silver platter. Also LOL about him being able to make an invisible rasengan without even trying to do so. Really shows hard work and now his forced seal from a forced ghost because he beat the villain in a forced fight is going to give him a major power up that puts him at a completely different level than his peers. I mean we could not have him work hard and still only be around his peers level since unlike Naruto he does not have the Kyubi to become hax. He needs the ghost seal in order to show just how special he is.
It is not forced when it sets up Boruto to be really talented shinobi with his expertise in Ninjutsu and his assets which even Sasuke himself acknowledges him from the moment Bolt threw the rasengan that already surpasses his previous predecessor. Sasuke knew if Boruto is so determine instead of taking shortcuts and his lack of enthusiasm then he would've been really competent shinobi since he was refered as a prodigy.
Sasuke trusted Boruto cause he had a trump card to save him, Naruto and the kages if they were all screwed.
A: Sasuke knew Momoshiki will catch off guard because the gap between with the Kid is completely immeasurable
B: Sasuke believed in Boruto talent knowing his proficient skills in adapting techniques such as Vanashing Rasengan will put to the rest if Sasuke and the others were to fall.
First used Vanashing Rasengan which completely bypasses Byakugan and 3 Sharinnegan and saved Naruto/Sasuke ass as well as the kages. Naruto was pinned down by the chakra rod which restrained him so he entrusted his son. Then Bolt somehow manage to
AMASSES Huge Rasengan (The biggest Rasengan from the likes we have never seen) despite having low chakra reserve; perhaps his hyuga bloodline runs deep. Then Sasuke created a diversion then proceed Boruto to do the rest. Bolt completely outsmarted Momoshiki by stabbing his rinnegan and then finish him off.
Like I said Bolt did some work.
If Boruto wasn't there 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.
Boruto did not autmatically gets powerup instead his result of sensing Momoshiki was because of the hyuga bloodline. Momoshiki's spirit acknowledged his potential and role in his defeat albeit grudgingly and cursed him along with the mark. Momo directly gave him his curse power which is DORMANT and he cannot use it freely without knowledge and training involve. Furthermore, it's not free when there is a price to be made to use the power. Sasuke didn't beat orochimaru yet gets a Curse Mark, such hyprocrite you are.