As @Dr. Nice said Shang-Chi is the only pure Kung Fu user so he wins be default.

I guess you could say

Not everybody was kung-fu fighting

Kung fu panda is goated

For a second I thought the image to the far left was Larfleeze the Orange Lantern of Avarice 😄

Why doesn’t Iron Fist count? He learns martial arts in China. King fu is Chinese martial arts

Danny trained in K'un-Lun and mastered their exclusive martial arts. He incorporates earthly martial arts like Kung Fu, Muy Thai etc. But he mainly uses K'un-Lun martial arts.

Shang-chi ☯️🥋🇨🇳

I'd have do go with Shang-Chi

Shang chi. However, iron fist vs him might be a good fight.

Shang-Chi