I have no experience of Fixer or Optimum so I can't offer anything with regards to those. Ultrafina, as you've found, doesn't have a great deal of cut - it's okay for light wash marring, but it won't remove deeper swirls or scratches. You should get a bit more cut from pairing it with the yellow 3M pad, which itself has more cut than the blue pad.
I doubt you'll need to use Fast Cut, I would have expected Extra Fine on the yellow pad (by DA) to remove a lot, if not all, the swirls perhaps stepping down to the blue pad. You can should then be able to refine with Ultrafina on a blue pad if you wanted to for that extra gloss.
Unfortunately, as already stated above, it's very soft paint so is extremely easy to inflict marring which is partly why I like to use a glaze. I know what you mean though, it can be quite disheartening at times though.