At @decrescendo's suggestion.
MBTI is an identifier of cognitive pattern preferences - ways in which we prefer to process information. Enneatype identifies overly utilized defense strategies - ways in which our minds overcompensate in attempting to protect our egos from harm. We know that there are three instinctual variants, self-preservation, social, and sexual, and that they have evolved out of biological survival strategies. But what, exactly, do they measure?
Recently in reconsidering my own type from sx/so to so/sx I have realized that I made the mistake of assuming instinctual variant to be a direct prioritization of goals - self-preservation types prioritizing resources; social types prioritizing interaction; sexual types prioritizing intensity. However, with input from others, I began to see instinct more as describing not necessarily what a person values most or acts on most but rather what a person feels compelled to keep conscious track of - self-pres types keeping track of resources; social types keeping track of interactions; sexual types keeping track of intensity. A dominant strategy in determining a person's instinct seems to be in "feeling out" their energy, moreso than a drier method of precise categorization f thoughts, behaviors, or feelings, which suggests to me that instinctual variant is widely recognized but not necessarily well defined.
Does anyone have any thoughts to add in terms of defining what instinctual variant is "measuring", or identifying?