The thing about auto fill, is it isn't just about role preference. At least, it isn't just about role preference. It's about overall match quality.
What people don't understand is that the longer a queue goes, the less strict the matchmaking becomes. It'll let greater differences of MMR be between the teams. It may adjust the LP accordingly per player based off their MMR, but this combined with premades is why we have auto fill, to help reduce cases where diamonds are against golds or similarly egregious cases.
The only reason it's occurring now is because of preseason resetting everyone's MMR, and because the population at the top of the ladder is smaller there's often not enough players to group the previously high mmr players together. It just doesn't work like that.
Now while I don't like being autofilled, I do believe that every person should be able to play every role somewhat competently. I don't mean that you should be able to carry with every role, but you should be competent enough to farm and not feed your lane. Going even or a little behind is okay if it's not your main roles, we're all human and it happens.
The main reason overall match quality is degraded is honestly because we've been spoiled for the past year of only having to play two roles. I think a decent compromise is to have a selection of three roles in parties of two or less. This way we have much greater flexibility and it may help players who aren't one tricks have variety. Just have primary and secondary, with tertiary essentially being your "auto fill" role.
