Autofill has no place in Ranked
The vast majority of high ranked players are role or champion mains. There is no place in a competitive game mode for forcing players to play with a handicap. The outcome is exactly the same as if they were outright forced to play a particular champion that they don't know.
Lower queue times is a fine goal for norms. That's for fun. People are eager to play. But if you don't have the time to wait an extra minute or two for a Ranked game, you shouldn't be playing ranked.
And if queue times are so much higher without forcing people to play Support, Riot, then maybe something needs to be done about the support role. But asking them to balance the game is too much, right?