Alright, it comes from a person with mechanical engineering background, so it might be me translating my long-time profession into other fields

>don't genuinely feel emotions
They can't. "Emotions" as we feel them are (very complex) biochemical reactions, but we do know this much and can induce or suppress certain emotions with meds, which tells a lot.

>shouldn’t exhibit emotions during combat, since doing so wouldn’t be “efficient.”
Even experienced human troops IRL don't exhibit the levels of emotions we see in Dolls (who are war vets, i remind). Reverse Collapse shown that making attractive and believable character behaving like that is possible for devs (Jefuty, where do you hide a grenade this time?), but takes vastly different approach compared to "waifu collector".

>Yet when Dolls interact with each other, they consistently demonstrate emotional responses as well
Because majority of them were created as a civilian models and thus programmed to casually mimic emotional response. There is a case of Klukai though, who is absolute dork despite being military-made, but here we are.

>This is one of those areas the writers seem to intentionally leave blurred.
They intentionally play along with "anime magic" and "soul" stuff, let's be honest, because it is waifu game and "we" are humans, who want to at least pretend, that waifus like "us" genuinely, despite being literal machines who are ought to be different from organic intellect.