Rhonin correctly explained the matchmaking system it’s been common knowledge since the start of the game that matchmaking system makes the game harder for you after your MMR goes up. It is designed to be that way. Unfortunately often giving you team low MMR players to balance the game means you then have to carry first pick Nova’s and trolls to win the game which is usually harder than playing against people who are better.
OP - you can’t draw conclusions on such a small data set. 3 games does not give you enough data to prove your assertions and in any event the matchmaking in HOTS is pretty clear and yes it can feel unfair.