Hrm.
The Diamond changes make sense. That is, you might get a role other than the 2 selected. And that's because as you go up higher in rank, players specialize in 1-2 roles, so top/mid/bot being popular enough, it would simply be inefficient and increase the queue times by restricting those players to those two roles. Yes, it's counter intuitive to what the system is supposed to be there for, but in high elos there's no other choice to lower queue times.
They're remedying this by decreasing the amount of players you can queue upwith down to 3, but IMO they should just revert Diamond+ to 'solo' queue. That is, 2 people at the most or, 1 player would be the best. If Dynamic queue is there for more casual players, than if you're diamond you're not a casual player, so lowering the amount of people who queue up together will lessen the queue times, maybe even remove the role selection in D3+(Again, if you've reached that far, then it makes sense that you'd have a good knowledge of all roles in order to compete at that high level.)
Granted that would mean that those who specialized in 1 or 2 roles would have a harder time getting D1+, but that's what differentiates the good players versus the bad, nein?