That's fair... but I do think that Celeste and Phoebe (I don't know about Katsumi) are a bit different from Juliette.
As you know, Juliette has this scene:
I don't recall Phoebe or Celeste ever showing even a hint of compassion towards anyone beneath them. If Juliette was just going to immediately turn Kane into shark food like she does with the vast majority of her slaves, would people still want a route with her? I don't think so.
tl;dr:
It feels (to me at least) that Kane can have a pretty twisted (but long-term) slave/mistress relationship with Juliette. With Phoebe/Celeste it's just... death.
I kind of already said it above (my response to Silver), but basically there is light at the end of the tunnel for Kane on the loser track. One example is that Tess strongly implied that Veronica doesn't care so much about dom/sub, and will eventually see Kane either as a man that she loves or not. All the suffering will pay off later.
But for Celeste/Phoebe, there's no light at the end of the tunnel. They're just going to torment Kane until they eventually get bored of him and kill him.
I really can't imagine only playing one route. The contrast in perspectives the reader gets as slave/slaveowner is what makes the story so profound IMO.
As a slave, it's all so unfair. As a slaveowner, it's shocking how little you care.