> it was an awful version control system even compared to what else was available at the time (CVS and whatnot). For example, it didn't support the concept of "atomic commits".

Neither did CVS. That was one of the big sellers of Subversion (maybe even the seller)

CVS in essence was just remote access to RCS files, where each file was handled independently, which caused lots of trouble to recover a specific state of work, especially when including deleted (or even worse: replaced) files.