They released stats showing that there is no statistically relevant difference to win rate in warrior vs non-warrior teams, but that there is in support vs no support. That's why they changed the matchmaker to match sup with sup.
Regarding HL, rank doesn't matter. I'm 10w2l, rank 34, with an MMR substantially higher than my rank. I'm sure when I lose a game, someone could rage about "being matched with a 34", but the truth is we have the same MMR and thus belong in the game. I'm sure given that I've only played 12 games in HL, the MM has very low confidence about my actual MMR, so it'll fluctuate wildly over the next 20-30 games. The alternative to this system is making it a linear gain right from the start, and thus subjecting the bronze/silvers to frequent shitpumpings by better players as they grind through them like a cotton gin. As it stands, the MM got me out of the ridiculous newbie tier within 2 games.
Booze, whats your btag? I'd be curious to compare your rank/mmr to mine just to get a feel for how hotslog MMR matches rank.