Here's a list of FF2 levels I feel people may have a shot at improving on (based on my time splits):

6. Precarious Pearls (May require pearl RNG)

7. Showdown in the Shallows (Tight improvement still possible)

8. You are my Sunshine (You need to get lucky with Gold Herring Spawn)

9. Delving Deeper

10. Toxic Trouble (I hate this level lul)

11. Wrasse Reef

12. The Trouble with Tuna

13. Cavern Carnage

14. Fishy Foreshadowing

15. Mine, All Mine (Should have tried to get eaten at max size)

16. Hazards Abound

17. The Long Pursuit

18. Shallower Seas (A pretty bad time loss in my run)

19. Nightfall (Worst time loss in my run)

If you optimize some of these levels and optimize the rest, you should be able to reach for WR, depending on your average time per level (excluding skips, bonus stages or other outlier levels like Spot the Ink, Tricky Treats or Madhouse)