I just came across this thread and...well, roachboy explained the situation in a way I wouldn't have had the energy for (but ought to). So many questions and assumptions when it comes to the "great" composers. Yeesh.
So yeah I agree with roachboy.
To add...why do the great composers necessarily have to be symphonic composers?
My answer to the O.P. might be something like: "Nowhere. The later half of the 1900s hasn't had too much time to get into the history books yet."
By the way,
R.I.P. Derek Bailey