busybox xz does not support the z switch
-z, --compress Compress. This is the default operation mode when no operation mode option is specified, and no other operation mode is implied from the command name (for example, unxz implies --decompress).
It sounds like some scripts will use -z and busybox xz will just fail.
xz -z
xz: unrecognized option: z
BusyBox v1.31.1 () multi-call binary.
Usage: xz -d [-cfk] [FILE]...
Decompress FILE (or stdin)
-d Decompress
-c Write to stdout
-f Force
-k Keep input files