Pre ag people lived nearly as long as modern humans if they reached the age of 25. One of the primary reasons life expectancy went up in the past 100 years is infant mortality was reduced to almost zero. It used to be very common to lose a baby at birth. My own great grandmother lost triplets shortly after birth and my grandmother had a premature baby that didn't make it.

Vegans get cancer all the time. Haven't looked into effects of fungi on the body, but one thing that did increase dramatically after the advent of modern (20th century) AG is heart disease. In fact even in the past few decades it has skyrocketed. That's NOT because of meat. We eat less meat as a percentage of calories than 100 years ago and prior.

Hong Kong, before it was taken over by Communists, had one of the highest per capital beef consumption in the world (almost twice that of Americans) and they are #1 on the 2018 life expectancy list: https://en.m.wikipedia.org/wiki/List_of_countries_by_life_expectancy

And #3 in beef consumption: https://beef2live.com/story-world-beef-consumption-per-capita-ranking-countries-0-111634