I had to make time to comment on these comments about conductors, classic recordings, etc.
I have played in many orchestras for many, many years. Some good, some not. I've played with hundreds of conductors, some good, mostly bad. And here's what I've learned: a good conductor DOES influence the performance greatly, and yes, he can even emulate Bruno Walter, Leonard Bernstein, or whoever he fancies himself being. But copying Walter's tempi, dynamics, rubato, et al does not make it great. There is something else that is frankly undefinable. It cannot be taught, and it cannot be copied. When playing with some conductors, there are times when you feel like all of the brains of the orchestra are somehow wired into the conductor and true magic happens. It's almost like ESP, I guess. Unless you've been there, it's hard to understand, but it is very real. A lousy conductor can make the Vienna Phil sound terrible -- and when they sound terrible, it's really bad. But a great conductor can make them play like gods. And the same goes for lesser orchestras. One orchestra I played with years ago was decent, but not top notch. One concert we did with a guest conductor. Within minutes, the whole orchestra sounded different. We played together, in tune, and you could feel the excitement. I cannot explain how he did it: it was Lukas Foss, but the way. The effect was electric. His baton technique is far from textbook perfect but it didn't matter. It's an amazing experience.
There are other orchestras that have such hallowed traditions that they refuse to play badly no matter what schmuck is on the podium. Cleveland is the most notable for this. They will not make ugly sounds, play out of tune or poorly regardless of what the conductor is doing. They play like a chamber ensemble; the Szell legacy is alive.
So what does this have to do with Mahler? Everything. Playing great Mahler takes more than fancy stick patterns, listening to Bernstein recordings, and emoting on the podium. I requires a deep, profound belief in the music that somehow is mysteriously conveyed to the orchestra. There are youngsters out there who get it, but not as many as I would wish.