I agree with the metadata changing under our feet but since
yum/dnf unless configured otherwise do not expire immediately
metadata, we could circumvent that issue.
Issue is that downloading metadata is not atomic: yum grabs
repodata/repomd.xml which includes relative links to the rest of
metadata. So using repo with "current" symlink would fail randomly.
You might say it's low probability but it is a race and it has been
seen in the practice.
Cheers,
Alan