Why Autofill doesn't "avoid excessive queue time" or "guarantee fair matches"

Autofill as an idea might sound great, you reduce queue time and you won't need to take someone with a widely different MMR and make an unfair match up. This, of course, might sound like a good idea for a non-competitive mode, where one would simply build AP Garen and try to enjoy the game, but doesn't work in ranked. It isn't uncommon for people to look at their teammate's main roles and decide that they will simply dodge a game if they see more than one auto-filled. there for you have a shorter queue time, but a longer time between champ select and the game. Which brings us to fairness, a fair game would be one in which both teams play at around the median of all Summoners MMR and each Summoner plays in their main role. In other words, an autofilled ADC vs an ADC main is not a fair match up. One has mastered the basics of playing their role, while the other hardly last hits. So please, why would an unfair match, with two or three dodges beforehand, be not a waste of time?