I've started going back through sections of the Gartenberg biography. I must say, I really prefer Gartenberg to Fischer. Although Fischer is far more detailed as a biography, Gartenberg comes to the point far faster than Fischer does. More importantly, Gartenberg is far better at discussing Mahler's music. In fact, Gartenberg is excellent at framing Mahler's music in context to those who came before and and after him: Beethoven, Schubert, Bruckner (great discussion of Bruckner) and Schoenberg. Fischer just keeps reaching for Adorno, which I think is just lazy and wrong.
When I return to Gartenberg, I begin to understand why it is that I was so disappointed with Fischer. Gartenberg is paced in a way that makes one understand that everything that happened in Mahler's life, really happened quite quickly. Fischer is so expansive and so detailed (mostly with negativity) as to make one feel that Mahler's life was one long expanse of drudgery and misery, driven along by psychological problems and character flaws. Furthermore, Fischer is really rather dismissive of Mahler's New York years from a musical standpoint. He doesn't seem to appreciate that it was in New York that Mahler had the most freedom in terms of programming for a symphony orchestra. This is no trivial point. Mahler became far more International and 'catholic' in his musical tastes: in a word, 'cosmopolitan'. Fischer finds only misery and exploitation in America - true to some extent, but not entirely accurate.