As we can see, the top 2 win rates are at about 3.5% above average (50%) while the bottom 2 are at 7-8% below average, a difference of at least two-fold. This means that Riot neglects certain champions and aren't concerned about how they are performing abysmally compared to the majority of other champions.

And finally for a look at the Challenger Division. This is the top 200 players in the NA region in terms of solo ranking.