I strongly believe that Percival has a special origin, I mean we know he's completely human but there needs to be something special about him otherwise it doesn't make sense, all the strong humans we've seen on the show so far were exceptions, Ban just stayed so strong by the fountain of youth, Escanor had Mael's grace, Merlin is only half human, and he was born in Belialuim, a renowned capital of mages, but what about Percival? What makes you so special? So special as to be stronger than the 7 deadly sins? It seems a bit far-fetched to say that he was born with rare magic, as we've never seen a human with such strong magic in the entire Nanatsu series, maybe Nakaba regretted making humans so weak, and now he wants to fix it with Percival , a strong human by itself and not by external means, but it still sounds a bit artificial and coming from nowhere. If I could make a guess I would say that maybe Percival has something to do with chaos, that would make everything more acceptable.