Developer insight on how players are matched, Year of the phoenix announcement saying that players will be matched using MMR, Blue post answering questions about matchmaking and explaining that the description of MMR in Battlegrounds similarly applies to Ranked. I wish we had access to the old forums because Jesse (the old community manager there) had on multiple occasions confirmed the same thing I’m telling you now.
“Players are paired using MMR”, is the official explanation, hence it is the status quo. Any claim to the contrary is laden with the burden of proof. As Madmax brought up, the “status quo” (that is, the set of likelihoods and distribution of games/draws that you’d expect from the system that Blizz claims) serves as the null hypothesis of whatever experiment you perform to test the randomness of the game.