I think I actually figured it out.

The reason rito has to keep dynamic queue around is because of the new champion select, and I bet they would have already reverted it if it wasn't. Why? Queue times.

Let me explain what dynamic queue does to queue times:

Multiple people queuing up together doesn't slow down matchmaking. It actually speeds it up quite a bit. This is because it forces people to pick at least 3 roles for a duo or up to 5 roles for a 4 man, forcing people to take the off roles and 5 mans mean that it only has to create one team.

Dynamic queue actually speeds up matchmaking.

The role selection of the new champion select, however, slows it down too much for dynamic queue to fix.

I'll try to explain it with completely made up numbers. Let's say of every 10 people who queue up, 3 want mid, 2 want top, 2 want jungle, 2 want adc, and 1 wants support. Completely made up the numbers. Now what the system did before if find the first 10 players to queue up and put them into a game, but now since there's only one support in those first 10 players, it has to wait for the NEXT support to queue up which could take another 10 players, doubling queue times for the first 10. The 9 players from the second set now have to wait for TWO MORE SUPPORTS, which triples their queue time and it goes on and on.

The only reason queue times aren't infinitely long is because dynamic queue forces 4 man premades to come with a support, along with 5 man premades, but it's still not enough to keep times under the 5 minute point from my experience and I'm only silver.

Now you see why riot HAS to keep dynamic queue. Because nobody wants the old champ select back. (Except myself and all the other former fill players out there.)

If I was unclear, tell me, and questions, ask them. Just wanted to share something I accidentally figured out.