Sejuani has a 78% W/R among Korean teams at worlds and a 67% W/R among chinese teams
And Koreans have the most Sejuani games played at worlds to.
Riot are you sure your nerfs go far enough on the PBE? We all know how hard LeBlanc, Rengar, Cassiopeia, or Syndra would be getting nerfed right now if any of their winrates approached levels that high or consistent in pro games.