Considering only the viewpoints inside the scientific consensus is limited - anyone as you said that practises the scientific method, whether in a formal institution, or not, should be able to have their view point considered. We should also never forget that there are politics in science too, and what's accepted is not always what is correct.
Scientists are subject to the human condition, just like anyone else.
I agree there are many snakeoil salesman, or kooks around. But I don't agree that the mainstream has the most optimal advice. In my personal experience I have been much more successful, in all my pursuits (health, programming, movement) by not following main stream advice, but rather seeking the minority that makes sense to me. In the words of Mark Twain, "The majority is always wrong, and the minority is sometimes right". I think the secret is finding the minority that aren't kooks, or snakeoil salesman. They do exist. I have found a few of them. Take the Ray Peat example. He didn't even know he had forums of people discussing his ideas. He doesn't even actively promote himself, or his ideas at all. I respectfully disagree that main stream advice is the most pragmatic.
I don't think the scientific community embraces the holistic nature of the world enough, as we tend to be dominated by linear thinking. If what you said were true, then we wouldn't have fields like Systems Thinking. It's definitely a niche area in research.
I also disagree about your comments on different diets. I have personally seen people religiously follow different diets, and do very badly on some, and well on others. I also prefer not to make statements like "People are not unique snowflakes" since I don't think we know enough at this stage. We are only beginning to understand the role of organisms in our gut for example, on overall health. I think your arguments here are too simplistic, and do not give a complex system like a human body enough credit. You should know that any simple answers to complex questions tend to be wrong.
Scientific consensus tends to be attached to formal institutions, not so? Formal institutions are then an authoritarian source. It comes from a position of authority. What you're essentially saying is something Government decreed for example, is not authoritarian, became it was enacted by a group of people. Obviously not true. Private individuals are generally less authoritarian, but they no doubt can be too. In this case, I am not aware of Ray Peat at all expressing his opinions as fact, but rather as something to be considered and questioned, like anything else.