I think it might work if pleasure reduced the circumstance penalty from trauma, in addition to its current effects. It's thematic since pleasure should make the chosen more receptive to other acts, and would mitigate the current issue pleasure has with harsh diminishing returns.
Seconding the Pleasure reduced Trauma penalties. Given that this is a game all about hard math and compounding multipliers, I've espoused before about how the fact that Injury is the only Circumstances that actually builds on itself positively is the reason why it's so utterly essential.
Hate is often included in these discussion as a useful too; but because Hate doesn't compound positively on it's own, it's only able to reach its probably potential when Injury is already in the picture. Similar with Expo; Bouncing Expo back and forth on its own between two chosen doesn't do a whole lot because its trauma strangles it so much.
In the scenario where Pleasure could soften Trauma's penalties to Circumstance, you could shift the number from Hate (or Expo) to the point where it builds on itself; and thus also adds positively to Pleasure too and support its growth. This makes fantastic sense because Hate and Pleasure combined lead to Inseminate; and provides the described situation in the narrative where the chosen are starting to enjoy it despite themselves and not resisting as much.
Injury would still remain one of the fastest ways to rapidly compound, but you'd want Pleasure in order to keep that ball rolling as well, and you'd be able to build at a slower rate with the other 3 stats for a no violence run. I think something to help with this overall numbers shift may be to reduce the dominance of Injury to compensate; if Pleasure provides a method to make Chosen more receptive and Trauma less hurtful, Injury doesn't need to leap out ahead on its own so much.
Without having run the numbers, it could be brought more in line to x3 / x2 instead of x4 x2 to narrow the extreme divide, since X4 x2 is actually functionally something like 4x the strength the effect of the x2 x4 from Hate.
Ultimately it just kind of stems from that weird balance between Trauma being both necessary for captures and also detrimental to the real circumstances you want to do, which is an awkward double duty to pull.
I also think disgust needs to be changed somehow, right now it's just worse than pain for chaining surrounds and no reasonable changes to pleasure or injury will change that. I don't have as clear of a suggestion for how to fix that, unfortunately.
Disgust is definitely unintuitive and finnicky, absolutely. The halving mechanic is perhaps a little too extreme in some middle cases, and helps contribute to Disgust / Pleasure being very poor; it has less returns on actual capture chance / time than even Injury does, despite Pleasure ostensibly being meant to set that up.
I almost wonder if rather than half, if the idea is to cap it it should be able to go up to the full defense level but no higher. Then you could at least create short openings by making the girls retch; but to keep them down, they need to be hurt, scared, or ashamed.
All in all the root of this Pleasure being undesirable problem is the heart of the game's struggle right now, since it's really sitting right in the middle of both making the game difficulty to learn as a game, and also obtuse / unapproachable as erotica.