But the population skill is a normal distribution. And for someone sitting on the right hand tail of the curve - there is a lot of area under the curve to their left.
The following simulation takes a population spread of 0 to 1800 and picks random players to be their opponents from a binomial (normal) distribtuion. It then compares them to a 'sweat' of MMR 1500 (the minimum for Onyx in Halo 5).
You can see why the very good players love random matchmaking. And because the opposite would hold true for someone on the left hand side of curve - you can see why this type of matchmaking struggles to retain new players.