Vegan versus keto diets is a false dichotomy. The biggest predictor of living a long healthy and happy life isn't diet or even exercise but relationships. What makes us sick in the modern world isn't because we eat meat or don't eat the correct vegetables. We are sick because we live in a highly toxic environment AND eat highly processed garbage (not biochemically and metabolically adapted to) AND we're losing our communities.
Metabolically compromised people can benefit from a diet fine-tailored to their individual condition (paleo to keto spectrum). People with autoimmune conditions can benefit from an elimination diet of which carnivore is a good pick. I have very close examples in my life of how a vegan diet can have horrendous consequences if you have the wrong undiagnosed autoimmune condition.
The last few decades have been riddled with bad science around diet and health in general. Let's not pray on the alter of Scientism. We can't take the health and lifespan of one set of religious people living in close communities in a clean environment and jump to the conclusion that it's only the consequence of their particular diet.