Heroes of the Storm ranked matchmaking win rates

So in theory HotS matchmaking is supposed to give players 50% win rate. I had however look at hero win rates at hotslogs and when filtered for bronze, silver and gold leagues no hero except Rehgar has win rate over 50% and it is even worse in lower leagues - in bronze no hero has over 45% win rate. Is there some kind of error in HotSlogs that I am not aware of or do lower league players just get shafted?