1. At first I thought you had an unused normal-hitnormal.wav but I saw that you used the sampleset overrides so it wasn't unused after all. However the override is quite tedious to set for multiple notes and there is a chance that you might forget to set it when you remap a couple notes during modding. If possible you might want to try and include the additional hitsound to the soft sampleset somehow. Maybe you could use a program to merge it with the existing whistle?
2. On that note, if your soft-hitwhistle.wav is exactly the same as the default soft sampleset, you can drop it from the song folder. Maybe you amplified the volume?
3. You could have your offset at 00:00:935 instead of negative.
4. Beat blankets like 00:14:050 (5,1) could be better executed to make a more perfect blanket. Use the approach circle of (1) as a guide (move (1) around in the timeline if you have to).
5. Make sure the combo colors aren't unreadably light/dark, especially against a background like that.

Your Good Self wrote:

There's nothing I can immediately see that's unrankable and unfixable.

Your patterns are what I like to call "clean and polished". That's a GREAT thing to have when mapping. The mapping style is definitely OK in my books.

Some issues you might want to take note of: (some of these might be unrankable issues but easily fixable)

1. At first I thought you had an unused normal-hitnormal.wav but I saw that you used the sampleset overrides so it wasn't unused after all. However the override is quite tedious to set for multiple notes and there is a chance that you might forget to set it when you remap a couple notes during modding. If possible you might want to try and include the additional hitsound to the soft sampleset somehow. Maybe you could use a program to merge it with the existing whistle?
2. On that note, if your soft-hitwhistle.wav is exactly the same as the default soft sampleset, you can drop it from the song folder. Maybe you amplified the volume?
3. You could have your offset at 00:00:935 instead of negative.
4. Beat blankets like 00:14:050 (5,1) could be better executed to make a more perfect blanket. Use the approach circle of (1) as a guide (move (1) around in the timeline if you have to).
5. Make sure the combo colors aren't unreadably light/dark, especially against a background like that.