Despite having published in nutrition journals I'm not emotionally invested in whether people agree with me about nutrition. But here are some thoughts on keto:

The keto diet had miraculous benefits for me. I've eaten only meat, seafood, and non-root vegetables 7 days a week, 365 days a year since 2019. Before that I was raised vegetarian (26 years), then experimented with paleo and following standard USDA advice. Before keto, I was very sick. After, I was healthy. Six years in, blood work is good. I can bench 2 plates.

I don't know what studies Cremieux is referring to (the link he provides is broken), and I haven't been following the scientific literature. But most studies I've seen cited to support the claim that keto is bad are observational studies that look for associations with lower carb or higher fat intake. That's not what keto is, and therefore not a test of the keto diet. Keto means you consistently restrict carbs and remain in ketosis.

Very few people have the discipline to actually follow the keto diet. So we're never going to have "a lot of data," even observational. Keto means no bread, sugar, potatoes, etc. It's not something you would attempt unless you were desperate. More than half of people who say they're "vegetarian" have eaten meat in the past week. I'd guess that the vast majority of people who claim to be on the keto diet cheat every day (i.e., are not on the keto diet).

There's no diet that can be optimized for every individual or for every outcome. When nutrition researchers find an alleged association between a dietary variable X and a health outcome O, they often declare that "X is good (or bad)" based on that. Even if the association is real (and this is usually impossible to actually establish), X might be good/bad with respect to O but not other outcomes. And X could have opposite effects in different people.

When I was doing work in nutrition I talked to an eminent researcher about the nature of nutrition science. (I won't name him because I don't know if he wants to be publicly associated with this idea. For what it's worth, he was a vegan for ethical reasons.) He said (quoting from memory): "Basic nutrition, like you need iron and certain vitamins, that's solid science. Besides that, there's a fermented fish from Asia that causes throat cancer. Processed meat is associated with colorectal cancer, but even that is uncertain. That's all we know."

I don't think that keto is optimized for longevity. (For that I'd bet on pescetarianism and calorie restriction.) And I wouldn't recommend it unless someone has a specific, serious issue. For me, keto is worth it for the short-term benefits even if I knew I would get coronary-artery disease and die at 72 like Dr. Atkins. However, nothing in nutrition science makes me think that keto makes that more likely to happen than if I were to follow the USDA's fake food pyramid.