Ken recovers far too quick after it is called off
He wanted it over and took a punch and stumble, and made sure to save his energy for his protest and post fight interview lol.
At the time they created a whole narrative about Sakuraba going to chute boxe and reinventing himself as a standup fighter, why his stance looked so different in this fight. So Ken going down from a punch in rd1 is consistent with the storyline.
Ken vs ROyce rubber match and Ken vs Rich Franklin were dives too btw.