Flex queue is a good way for riot to determine who has paid for boosting/account sharing
http://i.imgur.com/6AazcsN.png
and also
isnt the matchmaking supposed to give both teams roughly an even chance at winning ?
using those winrates red team (34+ 25 + 55+50 +24)/500 =37.6%
while the other team is (49+50+42+48+21)/500 =42%
Blue team has also collectively played ~1500+ more games than red team