LoL competitive play is always going to have a small champion pool
It's the nature of the game. For 1, some champs just work better in team oriented play. You're not going to see a Yi at worlds. He is too easy to shut down. That doesn't mean Yi needs buffed. 2nd, even if a champion is 0.00001% better than another champion, it's still going to be picked. They are being payed to play the game. So obviously, they are going to pick the champs that give them the best chance to do so. Sure, it sucks ass to watch the same champs being played over and over again. But in esports, they aren't playing the champs they like. They are playing the best champs at that time. But does that mean those are the only good champs and you can't win with anyone else in your silver elo game? Not even close. When a game is played at the level the pros play at, the tiniest difference is magnified. So even if the difference between champs is extremely small, they are going to be spammed.