There should be a matchmaking cut off. For example. If you have just started into comp (like me) you shouldn't be able to be placed again people with 2k points.
This matchmaking should be per rank. Not just looking for anybody. So guardians should play against guardians unless they are near the next rank. Once they get near they should be able to play both guardian rank and brave.
This then eliminates guardians matching against people in mythic or legend.