If distributing under 3(b) then it's legitimate to only supply source on request. Historically source has been distributed without revision control history or metadata and been considered acceptable (the source tarballs on gnu.org are snapshots, for instance) so I think the preferred form argument is also tricky. I agree that there's huge value in having the individual commits, but from a GPL perspective we had this argument when Red Hat started flattening all patches in the RHEL kernel source 15 years ago.