Actually Adoede that is something I figured out in the 2nd season

It basicly is a parabola, when you have low rating points you gain less and you lose less for wins, as you go along you start earning/losing more and more points and at some point these go down again.

This basicly comes down to the fact that when you are high up there at the end of the season at 8k+ or so points if I remember correctly ya are only gaining 2 points for a win and lose 1 for a loss