Halo 5 Arena "Ranks"

Can someone explain to me what is up with Halos “ranking” system? How can you even call it a system when you have unranked, gold, diamond, platinum AND onyx ranked players in the same exact game. That is almost every single rank in the game, and all playing in the same lobby. A lobby that is supposed to be matching people based on their rank. Now maybe I’m just late to the party here but someone has to have an explanation for this…