yeah i assume all the artifacts[0] and binaries greatly inflate that. I have no idea how git works under the hood as it is implemented at github, so i can't comment on potential reasons there.

Is there some command a git administrator can issue to see granular statistics, or is "du -sh" the best we can get?

0: i'm assuming a site-rip that only fetches the equivalent files to when you click the "zip download" button, not the releases, not the wikis, images, workers, gists, etc.