Remember that people play to win, not to prove their skill to anyone

People wonder why Tanks/Tanky Fighters are shitting on everything else. It's because they win, and quite effectively at that. People wonder why others play Tank and Tank is because they win. There's no reason to take Assassin Ekko mid where he'll struggle against the likes of Ahri, Zed, or Talon. Itemization wise, AD Assassins and ADCs are clearly favored. People don't play ranked to have fun or chill with their friends, they play to win. Remember that while the itemization and general balance of the game may be below the par for a lot of the player base, it is made to set clear cut winners and losers.