Was XZ used in parallelized fashion? Otherwise comparing is kind of pointless. Single threaded XZ decompression is way too slow.
I give thanks every day for pxz. I can churn out apt indices so much faster relative to the alternative.
For general purposes, I like using pixz which is indexable in comparison: https://github.com/vasi/pixz
Do you know if Debian is using parallelized XZ or not with apt / dpkg?