I believe that Party Based Matchmaking (PBM) has been absent in the latest FPS Halo installment, Halo 5. Without this matchmaking system, full teams of 4 can be put against full teams of randoms. This will almost always result in the team of 4 winning without any competition. This happens in Ranked and Social playlists alike. It happens so often that I rarely play Halo 5 when I am alone, I will not open the game unless my usual group needs a 4th or if I see them online and in a party.
Please, in the next Halo game, add this important feature for matchmaking back.