Riot logic behind changing a champion

"we think (X champion who does has a low pick and winrate) needs more counterplay, so we are going to remove most of their kit what makes them unique and make them a worse version of many other champions"

"We think (Y champion who dominates every single game, always first pick or ban) is a healthy champion, but some areas need to be toned down so we are going to reduce something what doesn't matter to the champion"