You know, Shawn, I used to think about about Haitink's recording of M8 on Philips too. But then I listened to the Pentatone remastering of it, and I completely changed my mind over it. I think it's a wonderful M8, with the exception of Haitink taking the ending of the "Chorus Mysticus" at an almost ridiculously fast pace. However, Haitink slowed that down a bit in his live 1988 performance that you can see and hear on Youtube. The visual element is absurdly dark looking, which is why I believe this has never made it onto DVD. Soprano Gwyneth Jones' contribution has been somewhat controversial, but I like what she does. Check it out and see what you think . . . . I think the difference between the original Philips issue and the Pentatone reissue of Haitink's first and only M8 recording, just goes to show how much sound quality really IS an issue with a work that has such a huge dynamic range, and a vast range of styles.
https://www.youtube.com/watch?v=vjbc5qrFJK8&t=832sAll that said, I completely agree with your overriding point. I don't think Mahler symphonies defeat people any more, but I think complete cycles can and do.