To be honest, matchmaking works a lot better than people think. Take me for example, after 250 wins in around 480 games I'm still in the Normal Pool, or as I like to call it, The Vanguard Pool.
Thovex uses his alt Maguuma to play with scrubs like me, after about 20 wins his alt made it into a higher pool than me. The matchmaking isn't done by win rate or KDA, it kind of watches the way you play and puts you in the right pool.
People complain about the enemy having hundreds of wins more than them but as I play more and more, I realise that it doesn't matter. I've had plenty of games where someone on my team has 800 - 1000 wins and they are utter shit and build Vanguard on every fucking hero.