Humans probably have wildly different nutrition needs depending on how physically active they are, how hot it is in their part of the globe, which foods are available in their area, their gut microbiome, etc.
Nutritional Science seems based on the idea that relatively minor tweaks to diet can influence health outcomes. After several decades of failing to find what those tweaks might be, it always seems strange to me that people don't seem to consider that they might just not exist, and that the human body is fine with whatever food it gets, within some broad range.
If you don't eat meat, it will be hard to get iron and B12 and carnitine and some other things. It will also be harder to get enough calories.
The metabolism of vitamin C in particular is pretty well understood, and no magical benefits of getting huge doses has ever been proven to have any of the claimed positive effects (despite many prominent supporters' efforts, including Mr Pauling).
Or for example I usually avoid sausage and fat meat as it is heavy on the stomach and weight. But the last days I have been in the mountains, walking over ice and snow. Fat meat was excellent, because with the cold, I burned lots of energy.
Also might have something to do with how many tens of millennia some peoples' isolated ancestors spent surviving on relatively limited local items available or cultivated, compared to what is now considered mainstream.
In my case I lowered my metabolism considerably so I could thrive in Texas without air conditioning in the summer. When everyone else was complaining about the heat this week, all I could do is remind them "it's not even summer yet".
Definitely was not as much progress during the first decade.