I can't speak to the '54 set, but I can speak to the issue of Jess Thomas. I'm not a fan. He's not bad, but he's clearly the one point to be discussed in an otherwise flawless set. To my mind, that issue is solved by the 1964 set, which has Jon Vickers' only Parsifal. The problem with '64 is that it's mono, which, then, presents one point to be discussed.
I'll say this, in my view, Knappertsbusch's 1964 represents the perfect storm: a perfect cast, a band that knew the material, a conductor with a solid grasp on the score, and the Festspielhaus acoustic. Knappertsbusch had 12 years to work on Parsifal on the Green Hill (Krauss had it in 1953), and, accordingly, at least in my mind, the '64 recording represents the high point.