That same thing happened to me . I joined a ranked match, ( I was level 12), and I got paired with level 5 and 4s. I was up against grandmasters. Please Professor Greyrose could you tell me why this happened?
The more players who are online and participating in the Player vs Player feature, the more closely the teams will be matched. When there are fewer players participating in the Player vs Player feature, the team members will be more varied and the differences between opponents will be larger.