So this means no otsutsuki invading the chunin exam? That was pretty much naruto & sasukes fight.
Naruto and Sasukes fight, but Boruto's story. The fight between Sasuke and the otsutsuki in the beginning only served to give the audience a sense of place. But it did not serve Boruto's personal story arc - which the manga is focusing on.
The chunin exams was a critical moment for Boruto's story arc because Boruto chose the "easy path" with the ninja tool and Naruto scolding him for that. Which only fueled Boruto's resentment towards Naruto. Then the bad guys come down to interrupt, Naruto and Sasuke try to hold them off and Naruto sacrifices himself for his son. This was another critical moment in Boruto's arc as this was the point in time where he realized how much he cares about his father and vice versa. Boruto volunteers to go and rescue his dad, and Sasuke takes him as his student to free Naruto.
And before you ask, yes. Even the end fight with Naruto and Sasuke against the villain was a core moment in Boruto's personal arc and deserves a spot in the manga while the opening fight does not. The whole movie was based around the old shinobi ways versus the new (hard work vs technology). The final fight paralleled this, as Boruto thought strength could be obtained through simple devices, and the villains of the movie were the symbolic embodiments of this (absorbing power to return it in brute force). However the villains were outdone by Naruto and Sasuke (hard work and teamwork), and Boruto chooses the old ways over technology to put in the final blow against the bad guy.