I don't get this at all. Either way you are duplicating the file. In the first situation, you duplicate it in the beginning. In the second situation, you duplicate it in the end. Neither way adds more steps. However, the new way is more clear about what you are actually doing and helps prevent the issue of overwriting your original.
If you duplicate up front, there is no chance of saving over a file by mistake. Duplicating in the end (save as) can have you forgetting that you were editing the original and if you hit CMD+S by mistake you end up overwriting.
The real reason a good number of people don't like Duplicate is because Human Beings are creatures of habit and people have being doing the Save As thing now for decades.
If you take a person who has never used either before, they will almost surely find Duplicate makes more sense and works better. That's because "Duplicate" is actually better and more clearer. "Save As" just has familiarity (for now).