The Fall of Badminton World Championship Winners

Well, regarding Men's Doubles, Women's Doubles, and Mixed Doubles, lower-ranked players did win the World Championships.
In Men's Doubles, Korea's Seo/Kim are overwhelmingly dominant, and the Chinese team that won the World Championships has never beaten Seo/Kim—mostly losing 2-0.
In Women's Doubles, it's China's Liu/Tan.
In Mixed Doubles, it's China's Feng/Huang, and various top-tier players won in a chaotic situation where they were ranked below them.