It isn't relevant to the point, which is that the capacity of doing something bad doesn't make you flawed. Whether or not 99.9999% of people are flawed doesn't factor into it, because the point of debate is whether mere agency in the world automatically makes you flawed.
Who says they did?
"Excelling" at something is generally speaking comparative. A top-of-the-line basketball player will still miss a ton of shots, but he still "excels" at basketball because the standard are regular people, whom he is way, way better than.
Like I said earlier, there is a near infinite potential for malice in the world. There are billions of ways for you to be cruel. Because of that, there must be something awful that you're as much better at than the average person as a pro basketball player is at basketball compared to the average person. You don't have to know it and you don't have to have done it, ever. You don't have to enjoy the act, just like Shirou excels at archery despite not finding any joy in it.
Yet, that makes you flawed?
^This guy gets it.