Not thinking much, I downloaded the v3 x86 linux-musl artefact onto our scicore cluster.

It turns out that on that cluster at least, the musl artefact does not get faster when increasing the number of processes with -j, in contrast to the gnu artefact (both downloaded from here: https://github.com/nextstrain/nextclade/releases/download/3.0.0-alpha.1/nextclade-x86_64-unknown-linux-musl https://github.com/nextstrain/nextclade/releases/download/3.0.0-alpha.1/nextclade-x86_64-unknown-linux-gnu)

The musl executable still keeps the CPU busy, it just doesn't seem to do any actual work.

For -j1 the difference between the two versions is small:

For -j10 it's huge: musl actually gets slower in real time, and consumes much more overall cpu time