i think there's a lot of noobstomping stuff in league (think riki/SA from dota).
the other thing is that if you have a stack, you get matched up with other stacks. so if you have a group of 3, they try to pair you against a team that has another group of 3.
lastly is that there is always an mmr, even in normals, so you tend to play against people matched up similar to your skill level, and starting out it is actually really volatile but eventually it will even out.
Every day's great at your Junes!