The Song Fight Bulletin Board

(and this still isn't the final mix)

I don't think anything actually improves in your before/after mix. In fact, something that is quite different from the sibilance gets lost in the after section, even though I'm not quite sure what. It just sounds flatter, I guess. Maybe due to other changes in the mix...?
I don't see the big deal, anyway... this is pretty normal sibilance. The main issues I see is are due to performance and arrangement:

• The "s" sounds at the ends of words are rather drawn out.
• There is little high-frequency content in the vocals, so the sibilance sticks out quite a bit
• The same is true for the rest of the arrangement: very low on high-frequency content, makes the sibilance stand out even more.

A quick listen to commercial mixes shows this level of sibilance is hardly unusual, it's just that usually the rest of the vocals is usually similarly active in higher frequencies, either through harmonics/formants, or through breathiness (whispery vocals).

For illustration of the performance aspect, I just recorded the one phrase a bunch of times, with a bit of reverb slapped on to make it slightly comparable. (Didn't think to record breathy vocals, sorry)

PS. a way to alter the sound of the sibilance to something that may appeal to you more is to widen the shape of your mouth/lips.

Hm, those are good points. Unfortunately I can't see how to get more of the high-frequency stuff without also changing the delivery - the singer is supposed to sound uncertain and wavery and so on in this song, because it's a very confusing situation that they're in. I could try putting more treble into the backing track, though, and try harder to reduce the length of the trailing esses.