What 5050BS says is actually quite true, there is no way to perfectly balance the teams out against each-other so one team will be given the edge team member wise. if you find yourself playing on blue side more than red side you are likely on the team with the lesser players as you either had some sort of winning streak or you are indeed the lesser player in the team.
This is sadly how it has been for quite a few years, i went 9/1 in placements and proceeded to get team after team of afks, leavers, feeders, trolls, and people who rather type than play, and in some matches i was soo tilted i was the worst of the bunch. I have legit been matched against people way above my rank just because i had a good placements session this year.
Now Riot plans to get rid of these boards making it harder for people to relay these issues to them and people who don't use twitter (me) or Reddit (me) don't WANT to be in their discord (again me) will have an even harder time finding people to play with .