"From the studies I read traumatic brain injury leads to a decrease in overall intelligence instead of selective abilities, doesn't it?"

Not so. The various parts of intelligence can be impacted differently. For example, my biggest deficit is verbal processing. My math skills are much better. I would have short term math deficits that I could overcome with training. I never could improve my verbal aptitude. Different skills use different areas and processing protocols. My verbal processing took a big hit 15 years ago from a mild concussion. I could no longer track characters in fiction writing and would get overwhelmed with overly descriptive writing. I ended up not renewing the magazine subscriptions I had.

The WAIS system of testing breaks down all these different functions. https://en.wikipedia.org/wiki/Wechsl...lligence_Scale

Research shows that a disparity between intelligence scales and memory,processing speed functions is indicative of an organic brain injury that happened after the intelligence was developed and matured.

My WAIS-II scales range from a high of 99% to a low of 88%. If you look at the bell curve/distribution of WAIS scales, you will see that is quite a differential. My WAIS-II processing speed was at 10%.
My Wechsler Memory scales are at 5% to 12% with one limited area at 22%.

The psychologist who tested me and wrote the report rejected the disparity as faking. He position was "How can someone with 88 to 99% intelligence have such low memory functions? " btw, My validity scores were 48 and 49 out of 50. Scores below 37 show possible faking.

All this to say that traumatic brain injury can cause disparate levels of function.

Regarding loss claims. If your injury caused you to have to settle for a lower paying job, that could be considered. It would be hard to prove. Trying to establish a monetary value to compensate for your psychiatric struggles would be difficult.

I think it would be extremely difficult to find a specialist who could order and then interpret imaging to directly point to your struggles, especially at 12 years post injury. Any damaged tissue would have be resorbed long ago. Small bleeds can be resorbed within a week or so. An fMRI could show functional weakness but, as I said before, would require finding a specialist with a database of normal functions. We have such a specialist in the US near Salt Lake City who claims to be able to diagnose against a normed database but their practice is unaffiliated with any research institution. I doubt any court or such would accept their report.

qEEG has the same problem. It can point to dysfunctions with statistical accuracy but is not accepted by our courts.

Research shows that severe injuries like yours often result in a failure for the brain to mature in judgement/decision making skills that usually mature during the late teens. That may be measurable with a full battery NeuroPsychological Assessment. From what you said, I don't think you had anything close to a full battery NPA.