Worst case, its still a better solo Q than the previous version.
In the past, you had 5 roles you MUST know how to play in order to get anywhere in league. You could be placed in any of these roles irregardless to anything besides your team's personal preference and the dreaded pick order. If you got last pick, you typically got support. If you got 3 or fourth pick, chances of you getting what you want is hazy at best. You could only really get what you wanted if you were first of second pick. This applied to all 5 members of your team simultaneously.
Now, you can have which ever two you like. You are virtually the old model's first or second pick all the time, except in select situations, someone might have to get the short end of the deal for the sake of getting things going. But 4 out of 5 players are still getting their first or second pick. No one is really getting put into their 3rd or 4th picks, and the only one getting the last pick is randomly generated.
So in essence, in the old model, as many as 6 out of the 10 players could end up with a role they didn't want. With the new one with auto fill, an absolute maximum of 2 will end up with a role they don't want. The other 8 are doing what they do best.