Honestly I wouldn't know anything about rock bands because I don't listen to it at all so you could be very right. I just responded because this thread was talking about string/barbershop quartets, which are almost definitely 4 parts because that is the minimum number of people required to make a 7th chord, and then again because you didn't know what a Big Band was, which I suppose is very understandable, but as somebody that grew up around and playing on them it's super foreign to me.