I hope riot will do something for next season about this.
Depending on your elo you will always have the same champions that are played.
In silver-Gold on top :
Nasus, Illaoi, darius, shen, camille
Warwick, Kayn, Kayn, Kayn and kayn..., Yi, xin, graves
Yasuo, Zed, Leblanc, zoé, Talon
Some seasons ago the diversity of characters played was way more random than about being ''OP'' or comfortable Characters to play.
A good thing would be to restrict players to play a certain number of times with a character per week and it will improve their diversity of playing and they will have to main more characters.