Interestingly, it may be an implementation detail, but the legacy Evernote client on macOS will "Save As" the file with Created date intact if the file was imported on that same machine with the legacy client. If it was imported on another machine, or it's a clean re-install and the notes sync'd down, then the Created date will be the current datetime when using "Save As".
On the new client it always sets the Created date to the current datetime regardless of whether the file was imported on the same machine or not.
Either way, would be great if it was possible for Evernote to keep track of the Created/Modified date for an imported file, and set things back to that state when using "Save As" so that the file is as imported.