What on earth is the ranked rating sysytem

I HAVE TEAMMATES IN DIAMONDS 2 and 3 AND THEY ARE BOTTOM FRAGGiNG SLAYER 2-18, HOW ON EARTH ARE THEY IN DIAMOND U GUYS HIGH OR SOMETHING AND GIVE EVERYONE DIAMOND RATING???

I imagine this’ll improve as more people get placed into the divisions - there isn’t a lot of info for the algorithm to work off just yet.