The gut-brain axis is highly influential in
normal every day depression. It makes sense why you
think this works for you.
I workout vigorously 3-4 times a week, try to avoid the regular bad stuff with diet, etc. It doesn't stop the adrenaline dump from being in an abusive relationship for a number of years when there's a minor problem, and it doesn't stop me from randomly having my brain completely shut down when I (unfortunately) remember some aspects of my childhood.
What has helped it CBT and time. The book in mention helped me understand why I feel the way I do, and that deeply rooted trauma (PTSD) exists as a misprogramming of your brain by a traumatic experience that is not "surface level" to trivially identify, and your brain is an excellent helper in compartmentalizing this for your own survival. Whether the information is wrong or right isn't what I care about. It's that it simply provided me a framework from which I could approach the problems I previously didn't really understand and led me on a journey of self discovery and bumpy healing I wouldn't have done otherwise. An inaccurate model is infinitely better than no model.
The author of the substack does an excellent job at taking something that we barely understand (psychology has a lot of problems of reproducibility) and generalizing it into a bullshit youtube short tier soundbite of an article with less information than the book he claims is nonsense. Reading his other article for reference I would be suspect of the author's credibility in any aspect of science other than the dangers of inhaling your own farts.
I especially the call back to another article of his that suggests that just loading up on exogenous testosterone is positively correlated with less PTSD. Funny enough I have had above-average testosterone through most of my life and yet I still managed to get a mild-to-medium form of PTSD.