Autofill is often making queues longer rather than shorter.
People often just end up dodging or trolling in champ select to cause someone to dodge. Instead of accomplishing what it's supposed to, it ends up making queues longer and games more toxic.
Also, this is a game, and games are supposed to be fun. Being forced into something you do not want to do is NOT fun. I don't mind playing support every now and then, but you should find a way to encourage people to play the role instead of forcing them into it.
So, remove autofill please. This would remove the uneven matches caused by having someone on your team being autofilled while their opponent wasn't.
EDIT : An example of a way to reward players for playing support would be to give a chest and a key to players that have played X amount of support games each 2 weeks.