I appreciate the passion and effort you're putting into your case, as you and others have said, you are entitled to administrative fairness and should be able to clearly understand the basis of a decision for which you disagree with and challenge it if it is incorrect. I don't want to engage in a giant point by point internet forum battle over your process, just give you some commentary from someone who has some general knowledge of an element of your problems.
To clarify on a small number of your points. All post fellowship doctors are specialists. Fellows of any specialist college and some senior trainees can undergo aviation medical training. Of that cohort some can go on to further post graduate qualifications and experience in the aerospace industry- generally, through the military and in the US or UK. There are some avenues for distance education and new courses in the Aus/NZ space recently. Australia has its own aerospace medical fellowship as well, the post nominals FACASM indicate that, earned after a number of years of study and assessment. There are very few surgeons with that dual qualification (I would say less than 10 in Aus, most of them eye, ortho and general surgery).
So when we play the game of "my opinion is better than yours" some of the weight will come from that specific expertise and as I said before, expert opinion alone is the lowest level of 'evidence' to support a decision. If there's no well designed study into your condition (and even better, a meta-analysis), in the aviation environment as well, then making a defensible decision will be hard, hence defaulting to a the general decision pathway for brain surgery/injury/interventions which does have this top level of evidence. There are even more complications when expertise on the condition, the environment and the safety system need to overlap, no one doctor is expert in all of them.
Using examples from non aviation contexts i.e. "I can drive a car so what if X" have not much relevance. The regulator is protecting the public from direct harm from aircraft crashes, protecting the industry with a perception of assisting rigorous safety management systems and setting a standard which is 'acceptable' to government, the public, industry and aircrew (in that order) Your car crashing into a pole vs shutting down an airfield or crashing into a house in western Sydney are obviously different levels of consequence (reductio ad absurdum on buses full of school children don't help you) and form part of the basis for differing standards to drive a car vs flying. Endless argument can be had over how automation and support systems have now altered what critical phases of flight is and the burden of the aviation environment on the body is little in recreational flying. Perhaps the standards will lower in the future, and they have already arguably with the introduction of the basic Class 2.
Undoubtably an unfair, or perception of an unfair, regulator will lead to lowered rates of compliance to 'protect' a privilege or avoid censure. This is not unique to aviation and applies to safety management universally. Processes and cultural changes need to be in place to avoid this as much as possible but again, universally, these do not tend to happen until after some critical failure and it is a thorny problem.
I felt I should put the previous and this here to assist the community in understanding some of the why/how in these kinds of cases, that do tend to appear each year or so. Being told you can no longer do something when you believe that it is the wrong decision is hard, it is distressing but it is not out of some systemic malice or malfeasance. It's a difficult decision (because there is no high quality evidence to support, because there are conflicting opinions from relevant subject experts and because it is in a population not flying Class 1- with the employment and industry pressures that may assist in gathering support) and no one would argue it is a perfect process.