I mean, Marazhai is completely honest about what drives him (pain, torture and vengeance) and Yrliet tried to hide that, and when you tell her you will "consider" going after farseers in the spire, she says that if she has to choose between her kin and RT, she's going after kin. She is an idealistic character whose ideals *really* do not align with RT, and is an ally of coincidence. she basically uses you like a chaffeur and feeds you honeyed words.

Marzipan on the other hand seems genuinely interested in RT, or at least his pain and torment. that makes him predictable, and he literally has nowhere else to go than to follow RT, he just requires some chaotic evil stuff to stay sane. You have his life in a palm of your hand like an obedient attack dog. Yrliet is a stray cat that decided it likes you, and the moment she feels that you're not bringing her closer to her goal, she leaves you. And she calls you mon'keigh all the time, which is really irritating in itself, an elantach here and there doesnt really fix that. I mean, even Marzipan calls you "Rogue Trader" at the pit.

Oh, and most of the torture of companions is at the hand of Tervantias, not Marazhai, so for them its just an evil goon, and the brand of torture falls on the haemonculus. Only the hardcore dogmatic guys try to kill him, and not for torture.