True, it is a very complex question, but I don't think it's hard to resolve. All you have to remember is composing then and composing now have almost no relation. Composition and interpretation and audience ambience have more to do what we know of jazz after 1950 now. I don't think creativity was really stubbed that much by whom they where hired by, it's more the limit of time and the occasion they had to compose for wich didctated some of the harmonic and rythmic content thus changing the mood for the occasion. I would love to talk more about it, it's a fascinating subject and I could finally put some of my musicology courses to good use.... well if you ever come to Montreal we' will have coffee and talk about it! good luck! Nick.