I think it's strange that Morton Feldman had such a low opinion of Beethoven. Convinced that Beethoven's music was structured solely according to functional tonal harmony, Feldman missed the most important aspect of Beethoven's work- a deeply organic expression of form, proportion, and scale; an aspect that Feldman's music shares.
While Beethoven's music in many ways exemplifies Common Practice tonality, the paths he takes to move from key area to key area show that, for him, balance and proportion are paramount. My favorite examples of this are in the first movement of the Waldstein sonata. Instead of stating the second theme in the key of the dominant (G major in this case), Beethoven finds his way to E major- not one, but four sharps away. What key, then, should the second theme be in when it's restated in the Recapitulation? It's supposed to be in the home key of C major, but Beethoven understood that the strangeness of the key area for this theme in the Exposition required a corresponding key of balance in the Recap. Since E major is the major version of the mediant, it would be satisfying to balance it with A major, the major version of the submediant- and that is exactly what Beethoven does.
The end of the Development section has another example of Beethoven's attention to proportion and balance. In order to prepare the listener for the return of the original key and first theme, it was customary for a composer to state thematic material on the dominant chord at the end of the Development section- the Dominant Pedal. In the Waldstein Development section, Beethoven never stays in one key for more than a few measures- usually just one or two. By the time we get to the end of the Development section, we have no idea where we are harmonically; we need a dominant pedal to make the arrival in the home key of C major satisfying and inevitable- Beethoven achieves this with a dominant pedal that lasts an entire page. (I love to point this out to my music theory students in order to show them that harmonic rhythm is often more important than harmonic progression). The longer this passage goes on, the more we crave the resolution.
The Development section itself has a counterpart that shows Beethoven's awareness of the importance of balance. The Development section is so long that it requires another slightly shorter development section at the end of the piece- more typically known as the Coda. There are examples of this- Coda-as-Balancing-2nd-Development- in many of Beethoven's pieces; it is a hallmark of his works in Sonata form. It's a product of his keen architectural awareness.
Morton Feldman was as keenly aware of architectural structures in his own music. He was a composer who was able to conceive of vast musical expanses of time and to create coherence and structural beauty within those expanses of time. Only a composer who had a deep sense of proportion and scale could compose pieces that last 4 hours (or more). Each gesture spins organically to the next in a way that always keeps one engaged; to my ears, not different from the way Beethoven, or Mahler, or Sibelius constructed their large-scale forms.
One of the most profound expressions of musical proportion and balance is in Hans Abrahamsen's Schnee. Schnee , for large ensemble, is made of 5 pairs of canons with three interludes. Each pair of canons gets shorter and shorter so that the piece seems at once like it's staying completely still while at the same time rushing towards an end point in the horizon. The interludes exist to achieve retunings within the ensemble. Abrahamsen has talked about trying to replicate the Doppler effect in this piece, both with the telescoping form as well as with the retunings in the Interludes. The lengths of the movements create a perfect sense of balance and scale, one that at the same time creates a profound sense of nostalgia and loss. (And, I think the one lone tam-tam strike happens at the Golden Section!)
I believe that the formal shape- the proportional map of the piece- is more important than any other aspect. The most beautiful or interesting sounds mean less without a clear, artistically meaningful container to put them in. In Beethoven, Feldman, Abrahamsen- just to mention a few- the brilliant attention to structure and shape is what makes the music so moving, so meaningful.