No, I wouldn't call Boruto a brat. I'd term him stubborn. Being the son of arguably the greatest shinobi/Hokage, Boruto is always known and accepted as his father's son. He feels that he has no identity for himself apart from being the 'Seventh's Son...!!!' which is why he despises his father. Naruto, who can take down an entire Zetsu army, fails at being a father because he himself had no father (Iruka, Jiraiya, Kakashi were close to father figures) and doesn't know how to acknowledge his child. Boruto despises that fact. He wants to rise above than being his father's son which he mistakes to be better than his father. Not only in terms of nature, but also in strength.
Boruto, like any kid, has a lot of love for his mother and Himawari and cannot stand to see them unhappy. So it's natural for him to feel that his father doesn't have time to spend with his family at important occasions like Himawari's birthday. He doesn't understand what it's to be a Hokage, at least until the later episodes where he remarks that he still hasn't understood his father yet.
In his mindset, he feels that becoming stronger than Naruto would be a great way to get back at Naruto. Knowing that his father has only one person who can match up to his level. He tries to learn from him.