That's generally true, but theoretically, pigz can extract single-member zip archives. I assume that they are both equally fast, assuming that they use zlib. libdeflate or ISA-L should speed this up significantly.
Furthermore, for compression, this still might be a valid question especially for the single-file case because it sounds like pzip parallelizes over the file members and cannot speed up compression/decompression of a single file member.
Furthermore, for compression, this still might be a valid question especially for the single-file case because it sounds like pzip parallelizes over the file members and cannot speed up compression/decompression of a single file member.