How about all of the plant-based athletes, then? See: Game Changers. Novak Djokovic, Tom Brady, Nate Diaz, Venus Williams, Scott Jurek, Kendrick Farris (the strongest American weightlifter at the 2016 Olympics), many members of the Tennessee Titans, etc. all follow a completely vegan or nearly-completely vegan diet.
Not saying vegan is the magic diet or best for being an elite-level athlete, but many high-level athletes follow a plant-based diet and are doing great.
Yes, all of those you mentioned ate meat for most of their lives growing up and working out building all the muscle and stamina. Then one fine day they decide to go Vegan/Vegetarian. Somehow all the foundation they built eating meat disappears. If you have any "Elite-level athlete" who has been a lifelong Vegan/Vegetarian, then we are talking.
Game Changers did a job marketing veganism but them referring to these athletes is a stupid thing they did, among other things, and lost credibility.
If I'm remembering correctly, there was one body builder on "Game Changers" that said he had never eaten meat in his life.