At the moment, trait Dominant is in game but acquiring it has been disabled due to malfunctioning code. It can be fixed by replacing the disabled code in newsexsystem.gd with this:

if lastaction.scene.code in sceneref.punishcategories && lastaction.takers.has(self) && person.asser >= 60:
    for giver in lastaction.scene.givers:
        if randf() >= 0.85 || person.effects.has("entranced"):
            giver.actionshad.addtraits.append("Dominant")

The Dominant trait does not appear to have been removed due to malfunctioning code, rather it was likely reworked as a birth trait rather than a trainable trait. Mav preferred to hoard old code rather than lose his previous work. (Edit: This hoarding is a bit less obvious now than it was a couple versions ago as I have deleted several of his hoards as I reworked various files, though I have created some new hoards as well.)  The game has been reworked many times over the years.