Most of the songs sound like things Charlie and Kadee would've actually wrote, whether it's minor details in the lyrics (Charlie proclaiming in "Someday" that he'll be "king of the Palace", the name of his family's restaurant) or highly reflective of their mindset ("Not So Different At All" essentially being a song Charlie wrote about himself and Kadee). Even "Nothing Gets Better Than This", which is sung in a Big-Lipped Alligator Moment, is more or less about how Charlie doesn't want to go home and finds comfort and enjoyment in the Pawn Shop.
In contrast, the songs characters are forced to sing have nothing to do with them; Kadee despises "Love You, Hate You" and Android is pretty much just a cover-band, with none of the artistic meaning behind the music and being purely manufactured for popularity's sake- showing how Kadee's father doesn't understand her, and how Arthur is cheap and uninterested in actual creativity. Similarly, Arthur sold Charlie's mother's piano and purchased a karaoke machine- another symbol of him prioritizing pre-written and already-popular music over artistic integrity.
At the end, Lloyd manages to go from being the second fiddle to his brother and an apparently bad dancer to one of Charlie's backup dancers, showcasing actual skill and timing that he lacked before. At first, it's just a surprise to see him randomly becoming good at dancing. On a second viewing it becomes more obvious: It's not Lloyd who's failing, it's that the dance isn't a very good one. Note how Andrew is never assumed to be the issue, and it becomes far more likely that Lloyd was always the more talented dancer, but was stifled by his family and unable to use his talent.
During the performance of "Not So Different At All", Kadee is visibly impressed, which is fitting because the song is about herself and Charlie, even if she doesn't realize it. However, another character who's impressed is Lloyd, who is also "not so different" from Charlie- they both suffer from the same Abusive Parent, both have the same ambition, and both get pushed around and mocked constantly. It only makes sense for Lloyd to be just as interested in the song- he can relate to it as well, especially when realizing that Charlie's the singer!