what riot doesn't tell you are these 2 things.
- they sacrifice good quality games for the sake of faster matchmaking.
- the longer you wait in the queue the broader they will search for abnormally higher/lower rated players
what this means is that if you play at abnormal times like 1am for instance, you are much more likely to be placed outside your range vs 4pm when all of the little kids get out from school and swarm the servers.
many people would opt for more balanced teams, i would MUCH rather prefer it myself, however separating these players who are willing to wait longer for better games would automatically raise queue times for both beyond what they could be in either direction.