Autofill punishes the players who don't dodge
Nothing is more frustrating than suffering through the longer queue times for mid/jg only to get 3 dodges and then be forced into support after 8 minutes by autofill. The players who have the benefit of shorter queue are the ones that should be getting autofilled, not the people who've been waiting around. It creates a perverse incentive to just dodge whenever something doesn't suit you, which lengthens queue for everyone else.
This obvious flaw would actually be funny if it didn't happen all the time