Whilst this is true, it might be of more interest to people to point to the sheer number of world class athletes of all types who have enhanced their performance by going vegan or near-vegan. A few examples are footballers like Messi and Aguero (both 'associated with a vegan diet' [BBC] but I'm mentioning them here because it's a football forum), plus many of the world's best endurance athletes such as legendary ultramarathoners Scott Jurek and Rich Roll, not to mention Eliud Kipchoge (although he does occasionally eat eggs as part of a meal) and 4 x marathon world record holder Fiona Oakes. Also strength athletes, e.g. a vegan carried the heaviest weight in history, holds the world record log lift, world record beer keg lifting, world record front hold... - no meat eater has ever been able to carry out these feats.
https://en.wikipedia.org/wiki/Patrik_Baboumian#Accomplishments
Then you've got the fighters. Mac Danzig (mixed martial arts cage fighting world champion), David Meyer (2 x Brazilian Jiu Jitsu world champion gold winner), plus loads more incredible athletes in all disciplines - too many to mention here.
The point is... Eat what you want, hold what views you want but to claim that being vegan can in some way impede your performance when many of the greatest athletes to ever live were/are vegan is so blatantly an invalid argument that you're better off just being more honest and saying that, despite any potential benefits, you are happy with your own diet and not interested in making any changes at the moment.