The biggest problem with Autofill
The biggest issue with autofill is one team has an autofill support and the other team doesn't. On average, an autofill support will not only be anywhere near as good as a regular support player; they will be toxic and give up 5 minutes into the game because they are doing something they don't want to. This makes ranked games severely imbalanced when this happens.
More people should want to play support, but autofill is not the answer. If no one wants to play it, CHANGE HOW THE ROLE PLAYS.