I've been using a Mac since it had only a Floppy drive and 128K of RAM, and I've been with various changes over time, and the "Save As..." function has been there all along. I know that the mission seems to be to make the filesystem less and less relevant to the "normal" user, exposing it only to "pros" but Save As... had a number of huge usability benefits over "duplicate" and over embedded versions.
While "Duplicate" is, in many ways, identical to "Save As..." what's not clear from that term and from the user experience is that when I duplicate a file, I'll also be prompted to locate the destination for the file in the filesystem. This is really important, as I get emails all day via Gmail that I need to open, review, modify and save, and so I open the file...Save As filename appending my name to the end, and then I put it in the folder for work in progress - basically all in the same interaction. Duplicate, while doing the same thing, isn't want I'm doing - a duplicate is a copy - the same thing - not the changed thing.
As far as rollback a version, incredibly, I've not figured that out yet. Some programs seem to have this, some don't, and I've not figured out why/which.
