The problem with pad conversion is that in most old gerber files there’s no way to find footprints. If the board file is meant to be modified, it would be meaningless to leave free floating pads there. The only way forward for the user is to create footprints and put them in their places and take away the old pads, whether they are SMD pads or holes. Therefore it doesn’t matter if the old pads are just holes.
Have you read Reverse engineering KiCad project from Gerber files?