Why they so harsh with Buddy?
My first impression of Buddy was actually better than Dusty character. He was motivated, enthusiastic, caring and even write songs for Dusty. On the other hand, Dusty looks tried, worn and unmotivated. Can be appreciated him gives tips to Dusty on how perform the song he wrote for him - the band was very rude by laugh at him. The affair with the Lula Rogers (Dusty manger) may not be ethical but it is not uncommon in music industry - the anger toward him smells feel righteousness. The song he wrote were good enough so we can give him a credit it's not because of the romance with Lula. Also he was kind enough to replace Dusty without anyone know it's him on stage. He took a big risk. I don't see in his request to ride at Dusty bus as something outrageous, it's was even make sense. Definitely he didn't deserve a punch to the face for that and after he saved them (!!).
Not surprise Buddy get angry at them. I would also.Maybe he was annoying person but that's all. In the first half of the film he didn't do anything wrong that make him deserve this bad treatment.
I Can understand why they angry at him latter when he interview about Dusty's disappearance. But even than they took thing too far, he's not the first guy ever that leaks information about backstage secrets, and still Dusty threatens him to never work in country industry ever again and ruin young singer career forever. It's was very cruel, mainly when it's clear that they enough money to overcome these embarrassment without losing the audience's trust. Lula have much more responsibility as a big boss and older woman.