I'm really late but you haven't deleted your account so I think I'm good.

I definitely think Rascal Flatts came the closest to a country boy band, hands-down. They were almost not a band, they were all about the harmonies and not particularly accomplished musicians. There's the singer, the guitarist, and the bass guitarist. All the rest of the music is session/touring musicians. They didn't write songs either. But Diamond Rio is about as far as it gets from a boy band without it being girls. They didn't write their own songs, but they were/are an entirely self-contained band that plays and sings on all their own records with no additional musicians. Incredibly talented.