Ok so the Qunari are Vulcans and the Tal Vashoth are Romulans?
I don't think so (even if I'm not a specialist of Stark Trek universe). It's more a matter of how the Followers of the Qun understand choices. As I understand the Qun, it isn't that one as never the choice, but more that the choices that are available to one depend strictly of previous choices, and usually, one set of choices will almost mechanically led to the other, and the set of choices which are outside one "reach" are supposedly provided by other Qunari : a warrior doesn't need to make his food when in Qun lands because a baker will do it for him, for instance.
An example :
There is a group of 5 children under a Tamassran. One was breed to be a worker and is female ("A"), two were breed to be warriors and are male ("B" and "C"), one was breed to be a priest ("D") and is female, one was breed to be worker and is male ("E").
During childhood, those children will make choices, both based on what they prefer in life, but also their personalities, so when they are 8 years old, we can have the following :
-"A" happens to prefer cooking over farming or fishing, always making the choice to attend baking courses, the Tamassran take note of that and orientated her toward this course of action
-"B" and "C" are both willing to partook in their warrior's training, but "B" isn't interested in more than the simple training, commanding and observations aren't to his likes, he makes the choice to eschew those to only train himself with the weapons, while "C" actually like the "ranger" training
-"D" is extremely serious in her studies and seems to be especially found of the complexity of the Qun sacred texts and interpretations; her Tamassran thus think she may be more fitted to the Ben-Hassrath than Tamassran
-"E" isn't interested in the manual labour but show great interest when it comes to the priesthood studies; also "E" doesn't really know if (s)he is a boy or a girl; the Tamassran make the choice to guide "E" toward the place he would be the more productive for the Qun, which happens to be the priesthood, therefore "E" is guided to assume that she is a girl, even if her body is the one of a boy. Also "E" seems to take a liking in learning how to help others discover who they really are.
Finally, least make another time-skip to when they are 22 :
-"A" is a baker and she makes food for the inhabitants of a settlement on Seheron; almost all of their choices are related to her work : how to cook what i was given by the fishermen ? What food use to up the morale of the inhabitants after a Vints' raid ? etc.
-"B" is a a Karasaad, a simple rank soldier, and his choice are mainly : How do I improve myself ? You note that the range of question and therefore choices is less important.
-"C" is a Sten in the Beresaad, and therefore, he has to make some choices : Does he learn the Common to better help the Antaam ? Should he trust those locals who hate the enemies he faces ? How could he ensure the victory of the Antaam ? etc.
-"D" is a philosopher, she has to think about the Qun itself : What does it means to be Viddathari ? To be a Qunari ? Should I treat foreigners this way, or this one ? Does this rule is actually too stringent and that one too lenient ? There is an extremely great amount of questions here.
-"E" is a Tamassaran; she has kids to teach, and it is a great responsibility : should she strictly guide the kids ? Or let them more freedom ? How can she be sure that she is making the better choices for the kid's future ? One more, there is a lot of questions and choices here.
Now, imagine that either of those five would turn its back on the Qun. Which would be the more probable ? I would say the soldiers, because they can be sent away from most of the Qunari for a long time. If the soldiers turn Tal-Vashoth, most of them don't know better than to kill because they never experienced a broad set of choics and questions in their lives -obviously, the higher the soldier is ranked, the more he has to make choices, and the more he will be able to become a correct Gray One and not a savage.
A Baker could turn Gray One, but it seems unlikely in most circumstances, because she would live sheltered in the Qunari lands. Nonetheless, should she become a Vashoth, she would either join the nearest band of "savages" and be kept as nothing more than a sex slave, or would manage to reach "correct" Gray Ones, and makes her life better, maybe.
A priest, either Ben-Hassrath or Tamassran wouldn't ever end with the "savages" because he/she would far too educated and used to various choices and questions and they would probably end as the core of a "correct" Tal-Vashoth group.
AT least, that how I think it would happen. Until we actually go to the Qunari lands to learn directly how they live without having to resort to the Antaam (or a Ben-Hassrath far from home), I would abide by this.