Below is the tail of building python on a system with 44 CPU cores and -j44,
it uses on average 1.08 cores out of 44.  If we could even average 4 cores
that would take the build time from over 2 hours to half an hour.

 dpkg-genbuildinfo -O../python3.13_3.13.3-2_amd64.buildinfo
 dpkg-genchanges -O../python3.13_3.13.3-2_amd64.changes
dpkg-genchanges: info: not including original source code in upload
 dpkg-source --after-build .
dpkg-buildpackage: info: binary and diff upload (original source NOT included)
7427.08user 591.11system 2:03:13elapsed 108%CPU (0avgtext+0avgdata 1826788maxresident)k
613480inputs+42264120outputs (594major+117907719minor)pagefaults 0swaps