White dude bros shouldn't be idolizing the joker, this was the director's goal (look it up).
It isn't shy about the fact it's a musical, it's a musical. I usually hate musicals because it takes so long to tell while someone is singing. This doesn't do that, it does both.
It's also highlighting that the joker is entirely insane. Are the songs even happening? It lays clear "the joker" is the shadow of Arthur who takes over. The joker has a music therapy session and latches onto that.