If that were true then how come it doesn’t relate to peak performance?

Your grandma is anecdotal so making that comparison to a professional athlete weakens your argument. On mass we know smoking has bad outcomes. But on mass eating carbs doesn’t.

We have entire cultures of people that never eat meat and sustain life just fine.

To further my point take the USA sports industry which is a multi billion dollar business that has every incentive to maximize human potential from an energy, performance, and endurance standpoint and yet sports trainers don’t put athletes on a 100% carnivore diet. Why is that? Are they all misinformed? They have the means to buy the best meat the world can offer and can implement these nutrition guidelines for all athletes but I haven’t heard of a single team doing this in all my years of watching sports.

I’m not trying to be a dick about this but I truly want to understand this position from a truth and evidence standpoint with real world examples not just cited papers and YouTube video of some doctor making meat be the cure all for human nutrition like with anything it has downsides and tradeoffs just like bitcoin.