The Dedra / mom stuff didn’t read as fantasy to me mainly because Dedra does not actually defend Syril’s character. There is in fact no sentiment in it at all.
I think the conversation actually explains the Dedra / Syril relationship perfectly: Dedra is a manager down to her very bones, so much so that “romance” with a rheumy-eyed, self-loathing milksop appeals to her. The management is the juice! Syril always folds under the slightest pressure, and thus serves as a perfect pez dispenser for when Dedra needs to soothe herself / get into her element by directing or controlling someone. She’s obviously not the kind of person who goes home to escape work.
The difference between her and the mom is that the mom is a purer kind of sadist, openly delighting in Syril’s misery, whereas to Dedra how he feels is entirely incidental. So far, at least. There’s an element of game-recognize-game in the way they talk frankly. And you can tell the mom is not just a little bit amused at meeting another, slightly different predator.
Dedra in that exchange is saying “your bullying is interfering with the way I run this relationship. Step off or get stepped on.” It’s all very psychosexual, but isn’t that always the way with Syril Karn?