People at the top of the charts in most cases write new songs for 3 days. That's why they have better rating. I would suggest to You to try instruct your band to write song for 3 days. Then we will see if it helps (I'm sure it will : ) ).
Well, You don't do anything differently, it's just solo bands are meant mostly for the rookie players to start the game. I have this question answered here. But the main point is that solo musician will always be in disadvantage compared to 5 members band, because solo band cost a lot less than 5 members.
I did updated the game not long ago to give some compensation, depending on what music style is selected. But this still didn't changed, that 5 member band is writing better song than solo band.
If You compare to the real life, there is always a group of producers behind solo musicians. Probably we could count on one hand solo musicians, who could managed to write a top notch album from a to z. Maybe, that's an idea for the game, like you can hire some additional persons, to help write and record songs. They could cost less and add less to the song than real band member. I will think about this. : )
I hope I answered your question. Let me know if not. : )
Band's rating (like manager's) is only used to determine chart position and it shows what was achieved here. Song rating isn't impacted by band's or manager's rating.
But the song level is determined by: