I’m a big fan of the books, having actually read most of the prequels (not Paul of Dune) and the sequels, so my interpretation may vary from that of movie version, so be warned.
IMHO, a bit of the problem comes from seeing the Bene Gesserit as either primarily social scientists, eugenicists, or seekers of true perfection of humanity. They are all of these things, or individuals are, but more, for all their disgust with and manipulation of religion, they are true believers.
They have evidence, in their own persons, of the ability to connect the past to the present, and wish to extend that to the future more clearly, while at the same time opening the history of the missing half of humanity via creating a male version of themselves.
So, again, it’s, at it’s core, not a vision that is fully rational, it’s a belief, a fervor, a drive which most if not all BG willingly sacrifice their own personal happiness and choices for for untold generations. And remember, especially if you’re a Reverend Mother, you REMEMBER all those sacrifices! Talk about self-reinforcing.
Which is why they absolutely test their own far more frequently than others. Almost no males are ever tested, because males are almost always seed carriers in the POV of the BG, not members, and lack the training and discipline to have the degree of self-control they require. Non-humans, to use the language of the test, may not further their goals, but their children, grandchildren, et al MAY.
So their is zero need to test most of those they seduce, bribe, or blackmail into donating.
So back to the question of what kind of people would be selected for IRL: fanatics and matyrs. IRL, if you test all those who follow your philosophy to chose death or mutilation before failure to abide by a directive, that’s the result. And, to some degree, it works. Add a religious motif to your duties, or a shared sense of shame, exclusivity, or the like, and you can create a (generally Very small) number of unthinking zealots who can be counted on to do anything in service of the group.
But I’m not sure they’re “more” human in the IRL sense, or more likely, less.
In the quite dystopian world of Dune, they cull their own quite harshly in all the societies we experience (Imperial House, Landsraad, BG, Guild, Fremen, etc). So to kill their own, much less others, is the norm. But for a less dystopian view, it isn’t all that different than Starfleets Kobyashi Maru scenario. Force a conflict on a human, between differing drives, and judge the results.