Ranked should consider the player's skill with their role when they get auto-filled.
Ranked should re-balance your team's average MMR to be lower if you have a player that gets autofilled into a role they don't know how to play.
For example: It's not fair to match an autofilled jungler against a main jungler within the same ELO.
EDITED FOR CLARITY:
Context: Ranked takes each player's MMR and finds the average, then finds you another team with a similar average MMR.
My suggestion: If a player gets auto-filled to a role they don't play, reduce how much of their MMR goes into the calculation that chooses their opponents. This will prevent unbalanced matchups due to one team having auto-filled and the other team not having it.
Going further, I think it would do a lot to help maintain balanced matchups if Riot would track players' MMR per role instead of just giving them a generic MMR to use for the above referenced calculations.
EDIT 2:
MordeCaiser raised a very good point here:
Yes but there are two aspects to the game:
- Skill for a champion
- Mechanics
Faker can play a champ he has never played and still have really good mechanics, but not much experience with the champ.
So maybe it would be best if Riot were to track MMR for several different categories, including role, mechanics, and possibly tactics?