It's untenable to consider ISO size alone. It is a legitimate concern, but it
can't be reasonable to soak every single CPU, times thousands. You're willing to
exchange less download time for longer install time and higher energy demand, but there
are quite a lot of other uses occurring that are relevant.
I don't have an immediate breakdown but RPM switching from xz to zstd increased RPM
sizes somewhat, but the installation performance makes up for the extra download time.