Autofill is solely a way to increase dodges. It does no good because of the massive number of people who just auto dodge when they get autofilled to support. It's very common to sit through 5-6 dodges (that doesn't even count afk checks failing) before getting a match and that equals an additional 7-10 mins of wait time anyhow.
The only reason for autofill is the support role that only 5% (at most) of players main. The simple and clearly the best and easiest choice is to make rift 4v4 and presto no more autofill, no more support and the game is 25% better all around.