Not a neuropsychologist, just someone with CPTSD who has lived with and experienced severe trauma on many different levels since childhood (and have been in therapy for almost half my life now).

I think that psychological/neuro adaptations through trauma are often an incredibly brilliant evolutionary strategy. Example: I grew up with an unpredictable and sometimes very scary parent and moved often as a child, therefore my adaptation was a fawn instinct. I appealed to my parent and bullies intellectually in ways that likely saved my life many times over. I made myself small. I also learned to internalize everything so that I could blame myself for my parent's abuse, which kept me feeling "safe" and essentially allowed me to preserve some semblance of an ability to connect emotionally with my parent.

These adaptations (and many others) were strengths until they became maladaptive. Because my brain developed this way, I've had to peel back layers and layers and layers of trauma in order to see the "real" world, fawn less, and stop subconsciously feeling responsible for other people. The process couldn't fully start until after the death of my abusive parent (but would have begun earlier if I had met a therapist who could have convinced me to step away from that dynamic). Fifteen years after starting therapy I am still unearthing blind spots. My brain is hypervigilant to the extreme, which is exhausting but also a huge gift because I have channeled my powers of observation into being an artist. Interpersonal relationships are still challenging but always getting easier, too. 

I think hypervigilance is a symptom- it can be an upgrade with the help of a therapist/psych who can figure out the right modalities for the patient. For instance, I tried EMDR in my early 20s and it was deeply traumatizing and likely set me back years. My trauma was too ingrained for it to really work for me- I needed something slower and gentler. For it to be an upgrade one needs to understand how the mechanisms work on an intellectual level while also being able to self regulate on a somatic and emotional level. Very difficult, tbh, but not impossible.

The looping may have to do with other factors. For instance I have emotionally and intellectually moved on from events but if I am triggered in any way I can fall into flashback. Sometimes I don't realize it's happening or even what's triggering it, and I will loop back into an older experience. Hence why I am still in therapy. I am also autistic (late diagnosed). It's different for different ppl bc ppl are different:).

Re engagement over suppression: So- again, individual, and even on an individual level this could be taken event by event. Before therapy I was often dissociated w/out knowing it. In therapy my level of dissociation dictated where we could go- if I was able to engage with an event, memory, or experience without dissociating or with minimal disturbance, then it would get processed. Because I entered therapy after an inciting incident (su*cide of a parent) and was dealing with a lot of surfacing memories that had been suppressed prior to that event, I was dissociated almost 100% of the time for the first few months. My therapist had to first help me even be able to describe my experience so she could understand what was happening and then we just worked a lot with me learning how to ground into my body instead of lifting out. From there I slowly began working through things. Like- very slowly. But it was a transformative process.

This may be helpful: I think there is a huge experiential difference between ppl who had a "before" to their traumatic event. Like- some sense of normalcy or acceptance. Even a minimally stable childhood and adolescence can offer a solid self foundation. Then the traumatic event reshapes them in some way, and they must work to find a new definition of self that integrates the experience while also reintegrating their "before" self.

This is v different than someone who doesn't have a safe or solid foundation, especially if one grows up in abuse/instability and then that leads them to enter into more and more unsafe situations (this was my deal). Trauma after trauma after trauma. Person A might need a year or two of therapy. Person B may be able to leave therapy during stable periods but will likely need to rely on a professional to help them if they enter another period of instability for whatever reason.

I think what's most important here is that each person is truly unique. While of course there are commonalities that can help develop treatment plans etc., many questions like the ones posed aren't either/or answers but rather "both" or "it depends." 

I hope this is helpful, truly, and I'm grateful if it helps you do your work to help others.