What do you mean with your first point? What does "All random. ALL random." mean?
Why are you biased against Fighters and Assasins? If you lob these two roles into a single slot then these roles will only see a 50% play rate verses the 100% play rate of the other roles. Which really sucks for people that like playing champions that belong to those roles.
By forcing people into a role you limit the possible matches the system can make which increases que times. For example, a player without support champions cannot be assigned the support role, you'll be adding the problems ranked ques are experiencing into aram (low number of players play support). I don't expect it to get as bad as in ranked (because this is more about owning a support champion rather then queing up as one) but it's still something to keep in mind. The problem might be solved with the free rotation always having champions available for every role but this will lead to a greater number of free rotation champions showing up in games leading to far less diverse matches.
Somebody else happened to make a simular topic, I also responded to him with other reasons why this would be a bad idea. Here's a link if you care to read it: https://boards.na.leagueoflegends.com/en/c/gameplay-balance/l84wz1rG-aram-shouldnt-be-completely-random-let-me-explain
