FWIW, I agree...Mahler changes the basic text far too often, and the old line about Schumann supposedly not being able to orchestrate has been blown wide open by several recent recordings (and even some older ones), so there is no need whatever to use the Mahler performing versions.
As a sidenote, I don't listen to Mahler (even though I was once an obsessive Mahlerian). I can't handle that level of spiritual nihilism anymore...
Well, to give some credit to Mahler, they didn't make a big fuss about those things in time... That's all positive I can say. Schumann did a work-over of Bach's Johannespassion...
He made Schumann boring and poor(!) and runined so many beautiful parts. The booklet of the CD is praising it and telling, how sensitive Mahler was bla bla but I don't think so.
I have the Gardiner and the Herreweghe-cycle (both are great but it's good to have them both), as well as Norrington, Bernstein and some others.
I never was a great Mahlerfan. I have some pieces I like but he never really got me. That Wagner/Bruckner/Mahler corner is just not my place. I'm more for Hans Neubahn and his friends.
Btw.: the fewer pieces you post the greater the chance anyone actually listens to them...