Ranking system question Gears Family

I’m wondering if anyone can tell me why is it that when I play TDM with my team(Ima Onyx 3 and they are onyx 1/2s) 8/10 games are against really low ranked players like bronze silver Gold etc? Reason I’m asking is because when I play by myself I play against good competition Onyx3/Diamond… but I’m confused because the ranking system is suppose to be team based so why when I play with my TEAM we play against really low ranking players and don’t move up at all/ Lose 8-10 percent if we lose a game, oppose to playing by myself with randoms who don’t communicate at all while playing better teams… I’m confused on that can any help?