@r1ggedgame
Well, you are correct that there are variables that make the matchmaking not totally random for players of the exact same rank which it should be IMO. In Respawns blog post about SBMM, they admitted that each players hidden elo affects the matchmaking even in ranked, which is ridiculous. They explicitly confirmed that if you are having good games, i.e you are over-performing at your current rank, you will be matched against higher elo players which usually means players who currently is a higher rank than yours. And likewise, if you are underperforming, you might be matched with players below your current rank etc etc. (So this is the reason why you sometimes see a "diamond" in gold lobbies. That diamond probably had multiple bad games with -60 RP and therefore dropped in ELO to average Gold)
BUT my point is that these rules are the same for everyone. You are not singled out in a ranked matchmaking specifically tailored to put YOU, one player among millions, in an disadvantage compared to all other players. Thats my point. We all play under the same rules. So if you cant reach, lets say Diamond4, then its not the system that is rigged because many other players manage to reach diamond 4 under the exact same matchmaking as you.
The only systematic unfairness that I can think of is that they sometimes match 3-man stacks vs squads of 1 solo + 1 premade duo. But in all honestly, I think the matchmaking is actually try to avoid this too. I rarely see obvious full 3-man stacks when I play solo and I can definitely see a difference in enemy teams coordination and teamwork when I play as a 3-man premade compared to when I solo Q