Enneagram isn't in-born (that's EIE lenses) but yes, it's developed over time based on the person's experiences so their enneagram becomes fixed in adulthood. At no point did Ichazo or Naranjo say that enneagrams is in-born. This is why they used the specific word "fixation" meaning that it's an obsession. You're not born obsessed. You become obsessed over time. That's not the same as cognition which is actually in-born, because that describes how the person is wired (although it doesn't describe why they're wired that way).
Yeah, I have my tritype, but I didn't figure it out. I had 5 duals and 2 identicals independently came up with my tritype. An identical, a benefactor, a supervisor, 2 duals, and 2 kindreds actually typed me as 8 core from knowing me for 2 or more years and they're very well versed in enneagrams. My enneagram and tritype doesn't determine my socionics type, since they're separate. Enneagrams talks about the ego's fears (mainly irrational fears) and taps into a person's emotions. That's not the same as thinking. Socionics explains a person's cognitive motivations. All enneagrams does is give another dimension to understanding a person but it doesn't explain how one set of fears can be "compatible" with another. Fear is fear. Some people can overcome them, some can't. Enneagram is totally self-focused, while Socionics is more about relations and society-focused.
I guess I am a "high" level Ti user, but I don't get pedantic and unlike Ti valuers, I don't care about finding endless info to answer a question that's already been answered before. If you're referring to the naturally hostile attitude people take towards their PoLR and equating it with fear and linking that to enneagram, then no, I'm not scared of Ti, however, it's still my PoLR. I'm just a subtype of SEE that has developed shadow functions. Some people who have developed PoLR functions don't get affected by it much, and for some, it's more intense. Enneagram may be able to explain why the individual has that level of intensity of being (negatively) affected by their PoLR, but doesn't determine it. I don't think I ever was scared of Ti, since my dad is LSI and he taught me Ti all my life. I work in the legal field, that's heavily Ti (but also Te) and I really enjoy it. This isn't to say that because I have developed Ti as SEE-N that another SEE-N is going to be at the same level of Ti development as I am. N subtype just means engagement with Ti, so whether Ti is the type's PoLR or lead, it doesn't matter, it is just a way to identify that the person has Ti accentuation.
One's mental health doesn't eradicate duality. It just happens. I've dualize with some who weren't at their best and over time we became friends. Duality doesn't mean there's an actual personal relationship, although it could develop into one over time. The point of duality is to provide each other assistance while one or both are in stressful situations. Think of it in terms of having an ally during tough times.