I believe fedpkg-minimal is needed for RPM builds because it is used to clone the dist-git repo and download the sources from the lookaside cache.

Didn't historically epel-release bring macro files which would be needed for build definitions? If that has been moved to other files, then epel-release would not be needed. The fedpkg-minimal I believe was required for the dist-git repo as @carlgeorge said.

Well, even fedpkg-minimal ... we need that for the "buildSRPMFromSCM" tasks (SRPM), not for the "buildArch" (RPM). Do those share the same minimal buildroot?

Hmm, per https://kojipkgs.fedoraproject.org//work/tasks/5463/78225463/root.log the RPM build does groupinstall build, while SRPM build does groupinstall srpm-build. So in my opinion, we could drop those from the build group, right?

After the prod->stg sync, we will test removing epel-release from both groups and fedpkg-minimal from the build group in staging

This is still needed for epel8-build, epel9-build, and epel9-next-build.

I tried to test this out in staging koji, but it seems that koji doesn't have a remove-group-pkg subcommand. I tried removing the srpm-build group and re-adding it without epel-release, but that didn't seem to have any effect. As soon as the srpm-build group is re-added, it already has all the same pkgs as before.

The group setup in koji is confusing... you want 'block-group-pkg' I think to remove a package.