Never said they flap at the speed of sound. Do you see the size of these wings.(
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). If Choji decides to flap these Lee get's thrown into the ground and punched to paste. Please a punch to the knee is going to hurt Choji l0l stop before i embarrass you. Choji punches will cause Lee to lose his balance seeing as these guys were blew back here.(
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).
He's gonna need attacks that are near the speed of sound to land an attack on Lee. Those wings aren't hitting him if Lee moves in close to Choji, and what's Choji going to hit to create that force that blew the other shinobi away? The ground? If Choji attempts that then Lee just jumps up his arm and carries on running until he gets to Choji's eyeballs, and no amount of durability is going to help Choji tank an attack to his eyes. Unless you wanna make a case saying his eyes also get durable too?
Gai literally sent the Mazo toppling over after he hit its little toe [
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], and the Mazo is much more durable than Choji. Lee can pretty much do the same or repeated attacks to Choji's ankle can yield the same result.