Mahler 10 a masterpiece... yes! and I raise my glass to this magnificent creation as well, even at 6:30 in the AM.
Mazzetti I, sadly no.
Although Slatkin plays the devil out of it, Mazzetti wisely withdrew this version with all the wild contrapuntal lines and garish over orchestration. He assisted Olsen with the Wheeler performances and then publicly stated that Wheeler "embodies the most authentic-sounding and unique realization of Mahler's last will and testament". He then does version # 2 that is a little less frenetic but certainly not as clear and spare as Wheeler. I am not a big fan of either Mazzetti version, but do share the opinion that Slatkin is a great Mahler 10 conductor and would love for him to do more. Rumor had it at one time that he was going to do his own version. Mazzetti did one thing very well, assigning the rising motif at the beginning of the finale to string bass and harp rather than tuba as in Cooke. The recording of Mazzetti II eliminated the second drum stroke which I prefer, but I am not sure if that is Lopez-Cobos' decision or Mazzetti.
It so comes down to how you view the work in Mahler's cannon. If you think, as I do (and I know it is mere speculation) that Mahler with the 10th was going in a new direction, then the work would be leaner, less orchestrated than previous works.
Regardless, it is one of Mahler's greatest works, one of the 20th century's great symphonies and one work I could not live without.