These people should be placed firmly in the first tier.
Back about 25 years ago, when Dr. Robert Winter did his Beethoven lectures at UCLA, he noted that people would often ask, "Why don't composers write like that today?" To illustrate an answer, Winter told a story about a trip to a used bookstore.
He had been looking for a copy of Goethe's "The Sorrows of Young Werther", but had been unable to find it. Instead he picked up a book called "The Snatch", which was a piece of porn about college girls kidnapped by terrorists -- and the sexual things they did to get away from said terrorists.
Winter noted that literature had changed, so it was to be expected that music would also change. He also noted the bloody history of the 20th Century and the move away from music that people could understand back in the early 20th. Music was now being written for academicians, not the people.
The classical canon may be a collection of musical museum pieces today, but they are a sampler of Western Civilization at its peak.
I think it's just a matter of the harmonic vocabulary being exhausted. There are only so many notes and chords in the diatonic scale. Even in the late 19th century people were expecting tonal music to eventually dissapear. Composers had to keep piling up more and more chromatic chords to refresh the ear. Tristan and Isolde was the beginning of the end of tonal music.
A relevent quote from Cosmic Moral Law:
Aïvonhov speaks from a tradition that recognized a continuum from nature to mind (or life) to spirit, with each transcending yet including the previous. Even in those rare times such a continuum is recognized, it's rarely recognized and understood as it once was; this difference in understanding is reflected in today's politics, science, religion, and art.... Take the case of musical geniuses such as Mozart or Beethoven: they were beings whose brain – or, rather, whose musical nerve centres – had attained such a degree of perfection that they could listen to melodies of the invisible world and, then, write them down on paper. To be sure, it is always possible to 'create' a certain kind of music; all you need is some knowledge of the laws of harmony. In fact, nowadays, music can even be made on computers. But that kind of music cannot give us anything. Many modern musicians are fascinated by these methods of compositions and, instead of rising to the highest regions of their soul in order to receive and record divine harmonies, they sink to a lower level and become more material. It is the machines that are making the music for them!Today's artists are no longer the inspired beings of the past whose first concern was to rise to a higher level and contemplate the beauty of the world above, before trying to express it through their art. In those days they would not begin to create until they sense that they were in communication with the Heavenly regions and had succeeded in contemplating its beauty. They respected and followed the rules of a certain discipline which they handed on to others. Whereas, today, artists have forgotten these traditions; each one works according to his own whims and fancies and it is the most eccentric that are considered to be the finest artists. The truth is that art demands that the artist be initiated, that he know the laws of the universe, for, without that knowledge, he can never be a creator.
- Spiritual Master Omraam Mikhaël Aïvonhov, 1968