Sure, Kakashi is present in the Boruto manga. His role might not be as prominent as in the Naruto series, but he still has significant moments and interactions.
Kakashi is very much alive in the Boruto manga. The manga doesn't include his death. Maybe you got some misinformation or confused it with another character's fate. But for sure, Kakashi is around.
In my opinion, Dumbledore would underestimate Harry Potter fanfiction. Fanfiction is a realm where fans take the original story and run with it in all kinds of directions. There are fanfictions that change the personalities of characters, create new storylines that deviate greatly from the original. Dumbledore, who is bound by the original narrative and his role in it, may not understand the significance of this new wave of creativity that fanfiction represents. He may see it as a distortion of the world he knows rather than a celebration and expansion of it.
No, Boruto is alive in the manga. The plot hasn't led to his death. However, the manga is ongoing, and anything could happen in the later developments.
Dumbledore might underestimate it because he's used to the 'official' version of the wizarding world. Fanfiction can be full of wild ideas that don't fit his traditional view.
Well, one reason could be that it's often seen as just a derivative work. People might think it can't be as good as the original series. But they're wrong. Fanfiction allows for so many creative interpretations. It can explore different character backstories, relationships in ways that the original might not have. It gives fans a chance to be creative and add their own ideas to the Harry Potter universe.
Well, 'Don't underestimate me' in MLP fanfic could refer to a character's determination to prove themselves despite initial doubts. It might also be a theme used to build tension and character development.